WBCHSE Class 12 Chemistry Polymers Notes

Polymer Chemistry Guide Class 12 Chemistry Unit 15 Polymers Polymers Introduction

Polymer Chemistry Guide: In the emerging world, it is impossible to spend a single day without polymers. The advent of polymers is the biggest boon to the chemical industry. Though the word ‘polymer’ is often used as a synonym for ‘plastic’ it refers to a large group of natural and synthetic materials.

• While substances like rubber, amber, wool, and silk form natural polymers, innumerable synthetic polymers touch different areas of our lives.
• We use synthetic polymers in clothes, tires, wrapping materials, bags, cookware, medicines and medical equipment, toys, and as lubricants and adhesives.
• They are also used in parts of automobiles and aircraft, microprocessors and computer screens, and various other electronic devices.
• This chapter gives an insight into the world of polymers. It discusses at length the various types of polymers, the way they are prepared, and their uses in our daily lives.

Polymer And Monomer

The word ‘polymer’ originates from the Greek words, ‘plus’, meaning many or much’ and ‘meres’, meaning ‘parts’. Thus polymer refers to a molecule with many parts. Polymers are molecules that consist of a long repeating chain of smaller units called monomers.

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Polymer And Monomer Definition: Giant molecules formed by the chemical union of a large number of small molecules, linked together in long chains of varying lengths, are called polymers. The small molecules forming the repeating units in polymers are called monomers.

where, n = no. of monomers present in a polymer chain. The value of ‘n ’ ranges from a few hundred to a few thousand.

Structural And Repeating Units Of Polymer

Structural Unit Of Polymers

Structural Unit Of Polymers Definition: It is the part of a monomer that forms a polymer. It is considered as the building block of a polymer chain.

Structural Unit Of Polymers Example: The structural unit of polyethylene (PE) is [—CH₂—CH₂—]. The polymer chain of polyethylene is formed by the repetition of this unit.

The structural unit of polyvinyl chloride (PVC) is The polymer chain of polyvinyl chloride is formed by the repetition of this unit.

Polyethylene terephthalate(PET) is produced from the monomers, ethylene glycol (HO—CH₂—CH₂—OH) and terephthalic acid (HOOC—C₆H₄—COOH). The two structural units present in PET are —O—CH₂—CH₂—O— and —CO—C₆H₄—CO—.

Repeating Unit Of Polymers

Repeating Unit Of Polymers Definition: It is the smallest monomeric unit of a polymer molecule that repeats itself to form the polymer chain.

Repeating Unit Of Polymers Example:

3. Repeating Unit Of Polyethylene Terephthalate:

Macromolecules And polymers: Scientist Staudinger introduced the word macromolecule to define a molecule having a molecular mass greater than 10,000. The molecular mass of the polymer lies between 10³ and 10⁷ microns.

• So, they are also called macromolecules or giant molecules. However, all macromolecules are not necessarily polymers. A polymer is made up of repeating monomeric units, while macromolecules do not necessarily need to have any repeating monomeric units.
• For instance, a polyethylene molecule which consists of repeating monomeric units [—CH₂—CH₂—] is both a polymer and a macromolecule.
• On the other hand, diamond, silica, and chlorophyll do not consist of any repeating unit. Therefore, they are macromolecules but not polymers.
• Hence, all polymers are macromolecules, but all macromolecules are not polymers. Oligomer: An oligomer is a molecule that is formed by the combination of a few (generally 2 to 10) repeating monomeric units.

Some Polymers, Their Monomers And Repeating Units:

Polymer Chemistry Guide Classification Of Polymers

Classification Based On Source

Based on source, polymers are of three categories—

Natural Polymer

Polymers that are obtained from nature (plants and animals) are called natural polymers.

Natural Polymer Example: Natural rubber, starch, cellulose, and protein.

1. Starch: It is obtained from α-D-glucose. Starch is present in roots, tuber (potatoes, arum), and seeds of plants. Plants store glucose in the form of starch which serves as a reserve of energy.
2. Cellulose: It is obtained from β-D-glucose. The chief constituent of the cell wall of plants is cellulose. 90% and 30-40% cellulose are present in cotton and wood respectively. Cellulose is also present in some animal tissues.
3. Proteins: These are obtained from α-amino acids and are mostly present in the protoplasm of plant and animal cells. Protein is essential for nutrition and growth. Natural silk and wool are proteins, which are used in making cloth.
4. Nucleic Acids: These are obtained from nucleotides. Example: RNA and DNA are nucleic acids.
5. Natural Rubber: It is obtained from unsaturated hydrocarbon, isoprene, or 2-methyl-1,3-butadiene. The latex (dense white liquid) of rubber plants is the source of natural rubber.
6. Biopolymer Starch: cellulose, protein, nucleic acids, and other polymers that control various life processes in plant and animal bodies are called biopolymers.

1. Synthetic Polymer: These polymers are artificially prepared in the laboratory.
   1. Synthetic Polymer Example: Polyethylene, polyvinyl chloride (PVC), polystyrene, polypropylene, nylon, and terylene.
2. Semi-synthetic Polymer: These polymers are obtained by chemical modification of natural polymers.
   1. Semi-synthetic Polymer Example: Cellulose nitrate, cellulose acetate, hydrogenated or halogenated natural rubber.

Classification Based On Method Of Polymerisation: The process by which polymers are prepared from monomers is known as polymerization. Depending on the mode of synthesis, polymers are classified as—

Chain Or Addition Polymer: The polymer which is produced by successive addition of monomer molecules through chain reaction without the formation of any byproduct is termed as addition or chain polymer and the process is known as addition polymerisation.

• Unsaturated hydrocarbons containing active double or triple bond(s) take part in this type of polymerisation.
• For such polymers, the empirical formulae of the repeating units are identical to that of the monomers.

Chain Or Addition Polymer Example: Polyethylene, polypropylene, polyvinyl chloride (PVC), polystyrene.

A few examples of chain or addition polymerisation:

Condensation Polymer: Polymers are formed when monomers with two or more functional groups are involved in stepwise condensation reactions with each other. In the reaction, small molecules like H₂O, NH₃, etc., are of the repeating units and the monomers are different.

Condensation Polymer Example: Polyamide, polycarbonate, polyphosphonate, polyester, etc.

Classification Based On Structure

Linear Polymer: Polymers that have long straight-chain structures are called linear or straight-chain polymers.

Molecular chains of such polymers are stacked over one another to form a well-packed structure. These have high molecular mass, density, and tensile strength and are soluble in organic solvents.

Linear Polymer Example: Nylon, polyester, polystyrene, polyvinyl chloride, and high-density polyethylene(HDPE).

Branched Polymer: Polymers containing secondary polymeric chains branching off the main chain are called branched polymers.

The melting point, density, and tensile strength of these polymers are low, while their solubilities are comparatively higher than those of linear polymers.

Branched Polymer Example: Low-density polyethylene(LDPE).

Network Or Cross-Linked Polymer: Polymers whose molecular chains are linked with each other directly or through a side chain are called network or cross-linked polymers. These are hard, brittle, insoluble, and infusible. Linear polymers can also be transformed into network polymers in the presence of a cross-linker.

Network Or Cross-Linked Polymer Example: Phenol formaldehyde resin, melamine formaldehyde resin, vulcanized rubber, epoxy resin.

Classification Based On Intermolecular Attractive Forces

• Different mechanical properties of polymers such as tensile strength, elasticity, toughness, etc., depend on the molecular forces operating between the molecular chains of polymers.
• In the case of polymers that are fully hydrocarbon in nature (for example., polyethylene, polystyrene, etc.), the only forces that operate between the molecular chains are van der Waals forces.
• On the other hand, in the case of polar polymers, forces due to hydrogen bonding in addition to van der Waals forces operate between the molecular chains.
• Based on the magnitude of intermolecular forces, polymers are classified as elastomers, fibers, thermoplastics, and thermosetting.

Elastomer: These are rubber-like substances and consist of randomly coiled molecular chains, held by weak van der Waals forces.

• These polymers can be stretched and deformed under stress. Branched polymer Ifa stress is applied, chains are straightened out and the polymer becomes stretched.
• When stress is removed, the polymer regains its original shape as the molecular chain returns to its randomly coiled state.
• This occurs because weak van der Waals forces are not able to maintain the stretched form of polymer. Elastomers have high molecular masses and are non-crystalline.
• They possess high elasticity and tensile strength. The tensile strength of an elastomer may vary from 300 psi to 3000 psi.

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Elastomer Example: Natural rubber, polyurethanes, polybutadiene, neoprene, silicone.

Fibre: These are closely packed long-chain polymers. The close-packing is due to intermolecular hydrogen bonding. Fibers are strong and hard and have high molecular mass and tensile strength.

Fibre Example: Cotton, silk, wool, jute, nylon, and terylene.

Thermoplastic Polymer: These are polymers that become soft and viscous on heating and again hard on cooling.

• This cycle of softening on heating and hardening on cooling can be repeated over and over again as desired without changing the properties of the polymer. These polymers are generally linear or slightly branched.
• The intermolecular forces of attraction in a thermoplastic polymer are stronger than those in an elastomer but weaker than those in a fibre.
• On heating these polymers can be molded into any desired shape which they retain on cooling.

Thermoplastic Polymer Example: Polyethylene, polypropylene, polyvinyl chloride, etc.

Thermosetting Polymer: These are polymers that soften on heating and become hard on cooling. But once they become hard, they cannot be further softened on heating.

• This is because chemical changes that occur on heating, convert it into an infusible substance. These polymers usually consist of molecular chains with a lot of branches.
• On heating, these branches react with each other, forming extensive cross-linkages between the molecular chains of the polymer.
• This results in a three-dimensional network structure, which cannot be remelted on heating.

Thermosetting Polymer Example: Phenol formaldehyde resin, epoxy resin, unsaturated polyester, etc.

Classification Based On The Arrangement Of Monomers: Polymers are of two types depending on the mode of arrangement of the monomeric units.

Homopolymer: Polymers that are composed of only one type of monomer molecule are known as homopolymers.

Homopolymer Example: Polyethylene, polypropylene, polyvinyl chloride (PVC), polystyrene.

Copolymer: Polymers that are composed of two or more different types of monomers are called copolymers.

Copolymer Example: Ethylene-propylene—a copolymer made of ethylene and propylene monomers, styrene-butadiene rubber (SBR)— a copolymer of styrene and butadiene, styrene-acrylonitrile (SAN)—a copolymer of styrene and acrylonitrile monomers, acrylonitrile-butadiene-styrene (ABS)—a copolymer of three monomers. Copolymers contain more than one repeating unit.

Differences Between Homopolymer And Copolymer:

General Characteristics Of Polymers

1. Polymers with high molecular mass are generally solid. Some of them are soft and flexible while others are hard and strong.
2. Polymers do not have specific molecular mass. The growth of a polymer chain during its formation depends upon the availability of the monomers in the reaction mixture.
3. Thus, the polymer sample contains molecular chains of varying lengths due to a variable number of monomeric units in them. Hence, the molecular mass of a polymer is always expressed as an average.
4. The density of polymers is much less than that of metallic substances. This is why, polymeric materials are light in weight.
5. Polymers may be transparent or opaque. Generally, they are colorless or sometimes white.
6. Polymers do not have a sharp melting point. The melting points of polymers generally lie between 100°-300°C. Polymers have lower melting points than metals or ceramic materials. Thus, the industrial production of polymers by molding is cost-effective.
7. The minimum temperature above which polymers like rubber become soft and elastic and below which they become hard, brittle, or glassy is called the glass transition temperature.
8. Polymers are generally insoluble in water but soluble in organic solvents.
9. Polymer solutions are highly viscous. The viscosity of even a very dilute solution of a polymeric substance is higher than that of the solvent due to the large difference in size between the polymer and solvent molecules.
10. Polymers are nonconductors of heat and electricity.

Polymer Chemistry Guide Methods Of Polymerisation

Methods Of Polymerisation Definition: A chemical reaction in which a large number of monomer molecules react to form a large polymer molecule of high molecular mass is known as polymerisation reaction. Two main types of polymerisation reactions are—

1. Addition or chain polymerisation,
2. Condensation or step polymerisation.

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Addition Or Chain Polymerisation

Chain Polymerisation Definition: The polymerisation reaction in which large polymeric chains are produced by the chain reaction of the same or different types of monomeric units is called addition or chain polymerisation.

Monomers Participating In Chain Polymerisation: Monomers having active carbon-carbon double bonds (such as ethylene, vinyl compounds, and so on) take part in additional polymerisation.

Monomers Participating In Chain Polymerisation Example:

1. Olefin compounds [ethylene (H₂C=CH₂), propylene (H₂C=CH—CH₃)],
2. vinyl compounds [vinyl chloride (H₂C=CHCl), vinyl acetate  (H₂C=CHOCOCH₃), acrylonitrile (H₂C=CH —CN), methyl methacrylate (H₂C=C(CH₂)CO₂CH₃), styrene (H₂C=CHC₆H₅)],
3. Allyl compounds [allyl chloride (H₂C=CHCH₂Cl) ],
4. Diene compounds [1,3-buta-diene (H₂C=CH—CH=CH₂)].

Repeating Unit Of Addition Or Chain Polymers

• In addition polymerisation, the monomer units are repeatedly added to the growing polymer chain without the elimination of any byproduct molecules.
• Hence, the formulae of the monomer and the repeating unit are identical and the polymer has the same empirical formula as its monomer.

Chain Polymers Example: The percentage composition and the empirical formula of polyethylene are the same as those of ethylene.

• The monomers participating in the chain polymerisation, are vinyl-type of compounds (H₂C=CH—X, where, X = Cl, OH, CN, CH₃, COOH, COOR, etc.).
• This is why the chain ‘ polymerisation is frequently referred to as vinyl polymerisation. This is also referred to as chain growth polymerisation due to the formation of growing chains.

Different Types Of Addition Polymerisation: For initiating an addition polymerisation reaction, a substance known as an ‘initiator’ is added to the monomer to activate the C=C bond present in the monomer.

• Initiator forms free radicals or cations or anions, which attach to the monomeric unit to form active intermediates, such as a free radical a carbonium ion, or a carbanion.

Depending on the nature of the intermediate, the addition polymerisation may be categorized into three types:

1. Free radical polymerisation,
2. Cationic polymerisation and
3. Anionic polymerisation.

Each of these polymerisations involves three steps—

1. Chain initiation,
2. Chain propagation,
3. Chain termination.

Free Radical Polymerisation: In this type of polymerisation, a thermally or photochemically active compound is used as an initiator.

Common Initiators Used In Free Radical Polymerisation:

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An initiator is an unstable compound. When it is heated or irradiated with UV or y -radiation, it undergoes homolytic decomposition, forming two fragments each of which contains one unpaired electron. These fragments with unpaired electrons are called free radicals.

Free Radical Polymerisation Example: Azobis-isobutyronitrile or benzoyl peroxide under¬goes homolytic cleavage to form free radicals.

To explain the various stages involved in radical polymerisation, let us consider an example, ethylene is converted to polyethylene by radical polymerisation.

Free Radical Polymerisation Chain Initiation: In the presence of UV or γ-radiation or when heated, the initiator molecule undergoes homolytic cleavage, resulting in the formation of two free radicals.

The presence of unpaired electrons makes the free radical unstable and chemically active. Hence, it readily reacts with a monomer forming the monomer free-radical.

Free Radical Polymerisation Chain Propagation: The monomer free radical combines with a new monomer molecule to form a dimer free radical. Similarly, the dimer forms a trimer, and so on. Thus, a long-growing chain of free radicals is formed till the radicals can add no more monomeric units.

Free Radical Polymerisation Chain Termination: The termination step comes after the propagation step. The long-chain radical loses its reactivity and any further addition of the monomer to the chain is hereafter stopped. The chain termination may occur in various ways:

Free Radical Polymerisation Coupling: Each growing free radical contains one unpaired electron. The unpaired electron of one growing chain may couple with the unpaired electron of another growing chain, thereby forming an electron pair.

• This leads to the formation of a covalent bond between the two chains. As a result, the reactivities of the two chains are nullified, and a dead polymer is formed.
• Since this process of termination involves the coupling of two unpaired electrons, it is called the termination of coupling.

Free Radical Polymerisation Disproportionation: In a disproportionation reaction between any two growing free radicals, the H-atom is transferred from one growing radical to the other. This results in the loss of reactivity of the radicals forming two dead polymer units.

Free Radical Polymerisation Chain Transfer: In this type of termination process, the reactivity of the growing radical is lost due to chain transfer, resulting in the formation of a dead polymer.

• These reactions occur in the presence of initiators, monomers, or solvent molecules that act as chain transfer agents.
• The growing radical loses its reactivity when H or any other atom is transferred from the chain transfer agent to the radical, forming a dead polymer.

• The chain transfer of the growing radical results in the formation of one free radical, which combines with the monomer unit and marks the beginning of a new chain reaction.
• Hence, in this reaction, one chain ends, while a new chain begins. It implies that the chain reaction gets transferred from one center to another. Hence, it is called a chain transfer reaction.
• Monomers taking part in free radical addition polymerisation: Ethylene, propylene, vinyl chloride, styrene, isoprene, butadiene, etc.

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Cationic Polymerisation

• The initiators used in these polymerisation reactions are considered to be catalysts since they are regenerated at the end of the reactions.
• Lewis acids (for example., BF₃, AlCl₃, SnCl₄, TiCl₄ ) are widely used as initiators in cationic polymerisation.
• Lewis acids can themselves initiate polymerisation. However, the reaction gets faster in the presence of a suitable source of proton (H⁺)  like water or alcohol.
• In that case, Lewis acid is referred to as a catalyst, while the proton source is the co-catalyst The vinyl monomers with an electropositive group take part in cationic polymerisation.
• To explain the various stages of cationic polymerisation, let us consider an example, the cationic polymerisation of isobutylene forming polyisobutylene.

Cationic Polymerisation Chain Initiation: In the presence of water, BF3 forms a hydrate that exists as an ion pair.

The H⁺ ion reacts with a molecule of isobutylene to form a carbonium ion, which marks the initiation of the chain reaction. The [F₃BOH]^– ion of the ion-pair exists as a counter ion along with the carbonium ion.

Cationic Polymerisation Chain Propagation: The carbonium ion thus obtained reacts with another isobutylene molecule to form a dimer carbonium ion. This newly formed ion further forms a trimer carbonium ion and thus results in a long chain of carbonium ions.

The growing long chain carbonium ion The growing long chain carbonium ion keeps combining with the monomer units till it loses its reactivity.

Cationic Polymerisation Chain Termination: The growing long-chain carbonium ion loses its reactivity either by disproportionation or coupling and eventually forms a dead polymer.

• Chain Termination Disproportionation: In this process, a proton(H⁺) is transferred from the carbonium ion to the counter-ion, forming a double bond at the end of the polymer chain. This reaction leads to the loss of reactivity of the carbonium ion. As a consequence, it forms a dead polymer.

Chain Termination Coupling: The reactivity of the growing long-chain carbonium ion is lost due to coupling between the growing long-chain carbonium ion with the counter ion, forming a dead polymer.

Monomers taking part in cationic addition polymerisation: Isobutylene, styrene, α-methyl styrene, vinyl ether, etc.

Anionic Polymerisation

• It involves polymerisation of vinyl monomers having strong electronegative groups (for example., —CN).
• In this type of polymerisation, the alkyl or aryl compounds of alkali metals [such as butyl lithium (BuLi), triphenylmethyl potassium (KCPh₃)], the amides of alkali metals [such as LiNH₂, KNH₂ ], grignard reagent, etc. are used as initiators.
• Acrylonitrile (H₂C=CH—CN) undergoes anionic polymerisation in the presence of butyl lithium(BuLi) to form polyacrylonitrile.
• The same reaction is considered to understand the mechanism of anionic polymerisation.

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Anionic Polymerisation Chain initiation: The butyl ion (Bu^–) of the initiator, butyl lithium (BuLi), combines with a molecule of acrylonitrile to form a carbanion, which initiates the chain reaction. Here, the Li⁺ ion acts as the counter ion or gegenion of the carbanion.

Anionic Polymerisation Chain Propagation: The carbanion combines with another molecule of acrylonitrile to form a dimer carbanion. Similarly, a dimer forms a trimer, and so on. Thus a long-growing chain of carbanion is formed by repeated addition of the monomer units.

Anionic Polymerisation Chain Termination: In anionic polymerisation, the termination does not occur unless some impurities are present in the reaction system or some impurities are deliberately added to the reaction system.

The presence of impurity causes nullification of the reactivity of the growing carbanion, resulting in the formation of a dead polymer.

• If the monomers that are used in polymerisation contain no impurities, then the reaction continues till all the monomers are exhausted.
• In such a case, the carbanion does not lose its reactivity. At the end of the reaction, if a fresh quantity of monomer is added to the reaction system, the polymerisation reaction again goes on until the added monomers are consumed.
• Since there is no loss in the reactivity of the carbanion in the absence of impurities, anionic polymerisation is also known as living polymerisation.
• Monomers taking part in anionic addition polymerisation: Acrylonitrile, styrene, butadiene, isoprene, etc.

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Polymer Chemistry Guide Condensation Or Step Polymerisation

Step Polymerisation Definition: A toiyrnerisation reaction in which two monomer molecules of the same or different types having at least two functional groups are joined together to form a large polymer chain is called condensation polymerisation.

• In this reaction, small molecules like water, and alcohol are obtained as by-product.
• This type of polymerisation involves stepwise addition of the monomeric units, resulting in stepwise growth of the chain. Hence, it is also known as step growth polymerisation.

Monomers In Polycondensation: The monomers participating in the polycondensation reaction must contain at least two active functional groups.

• Two different functional groups obtained from each monomer are joined by a condensation reaction.
• Thus, a large number of monomer molecules form a linear polymeric chain by mutual interaction. However, if there are more than two active functional groups in the monomers, then cross-linked or network polymers are produced.

Step Polymerisation Example: Terephthalic acid (HOOC—Ph—COOH) [monomers with two —COOH groups] and glycerol (CH₂OH—CHOH—CH₂OH) [three active functional groups] undergo polycondensation reaction to give cross-linked or network polymers.

Different Types Of Polycondensation

For any polycondensation, there should be at least two active functional groups present in the monomers.

A-B Type Of Polycondensation: If two functional groups present in the same monomer, react with one another to give a large polymer chain, then the reaction is termed self-polycondensation and is described as an A-B type of polycondensation.

A-B Type Of Polycondensation Example: p-aminobenzoic acid undergoes self-polycondensation or A-B type of polycondensation to form aromatic polyamide.

• In this type of polycondensation, both the active functional groups (—NH₂ and —COOH) are present in the same monomer.
• Here, the amino group (—NH₂) of one monomer combines with the carboxylic group (—COOH) of another to form an amide bond (—NHCO—), along with the elimination of a molecule of water.

The amide also containing an amino and a carboxylic group further reacts with a monomer to form another amide.

Thus, a large number of monomers join stepwise to form a long-chain polyamide molecule.

AA-BB Type Of Polycondensation: If two functional groups present in the same monomer do not react with one another, then polymers are not formed. However, if the monomer reacts with another monomer to form a polymer through polycondensation, then it is known as AA-BB type of polycondensation.

AA-BB Type Of Polycondensation Example: Terephthalic acid (HOOC—C₆H₄—COOH)  contains two carboxylic acid groups that do not react with one another.

• Hence, terephthalic acid does not form a polymer through self-polycondensation. In the same way, ethylene glycol [HO —(CH₂)₂—OH] does not undergo selfpolycondensation.
• However, ethylene glycol reacts with terephthalic acid to form an ester.

The ester molecule containing a hydroxyl and a carboxylic group reacts with a similar ester to form yet another ester.

Thus, a long chain of polyester (polyethylene terephthalate) is formed by a continuous reaction.

Differences Between Addition Polymerisation And Condensation Polymerisation:

Copolymerisation

Copolymerization Definition: A polymerisation reaction in which a large number of two or more different types of monomers react with one another to form a large polymeric unit is called copolymerisation. The polymers thus obtained are called copolymers.

Purpose Of Copolymerisation

• Consider two monomers A and B. Monomers of A on polymerisation form a homopolymer and those of B form a homopolymer.
• However, when a mixture of A and B undergoes polymerisation to form a copolymer, the resulting polymer has different chemical composition and molecular arrangement from those of the homopolymers.
• As a result, the properties of the copolymer obtained are also different from the homopolymers, and thus the desirable properties of the homopolymers can be infused into the copolymer.

Purpose Of Copolymerisation Example: Polystyrene (PS) is transparent, hard, durable, chemical resistant, and suitable for molding, but brittle.

• Polyacrylonitrile (PAN) on the other hand is hard, durable, chemical, and impact resistant, but not suitable for moulding.
• However, Styrene-acrylonitrile (SAN), formed by copolymerisation of styrene and acrylonitrile, is highly impact-resistant and extremely suitable for molding.

Different Methods Of Copolymerisation: Copolymerisation can be carried out through various methods. Industrially, these are produced by addition (free radical, cationic, or anionic) and condensation polymerisation.

1. Copolymers Produced By Addition Polymerisation: Styrene-butadiene rubber (SBR), Styrene-acrylonitrile (SAN) copolymer, Acrylonitrile-butadiene-styrene (ABS) copolymer, etc.
2. Copolymers Produced By Condensation Polymerisation: Unsaturated polyester (monomer:
   phthalic anhydride, maleic anhydride, propylene glycol), block polyamide (monomer: terepthalic acid, isophthalic acid, hexamethylene diamine) etc.

Widely Used Copolymers And Their Applications:

Some Important Polymers

Polythene Or Polyethylene (PE): Polythene or polyethylene is the simplest hydrocarbon polymer. The structural formula of this additional polymer is

Polythene is a widely used polymer and has the largest quantum of production. In 1933, Imperial Chemical Industries first started the production of polythene in England. Mainly two types of polythenes are produced commercially. These are—

1. Low-density polyethylene (LDPE) and
2. High-density polyethylene (HDPE).

Manufacturing Of Polyethylene

Monomer: Extremely pure ethylene is required as the monomer for the production of polyethylene.

• Ethylene is obtained by the partial hydrogenation of acetylene or by the dehydration of ethanol. Ethylene may also be produced by thermal or catalytic cracking of petroleum hydrocarbons.

Manufacturing Of The Low-density Polyethylene (LDPE): The free radical polymerisation of ethylene gas (99.9% pure) at high pressure (1000-3000 atm) and 170-250°C temperature in the presence of an oxygen initiator gives the low-density polyethylene.

• The reaction is exothermic (A/H= 105 kj.mol^-1). Hence, there is a possibility of explosion, if the heat liberated is not properly controlled.
• Ethylene used for preparing polythene should be extremely pure to ensure that the average molecular mass of the polymer is maintained.

Manufacturing Of The High-Density Polyethylene (HDPE): The polymerisation of pure ethylene at low pressure (3 -10 atm) and low temperature (70-100°C) in the presence of Ziegler-Natta catalyst results in the formation of high-density polyethylene.

Ziegler-Natta Catalyst: A mixture of triethyl aluminum [Al(C₂H₅)₃] and titanium tetrachloride (TiCl4) or diethyl aluminum chloride [Al(C₂H₅)₂Cl] and titanium 5 trichloride (TiCl₃) is called Ziegler-Natta catalyst.

Linear low-density polyethylene, (LLDPE): When pure ethylene mixed with a small amount of α-olefin (for example., 1- octene or, 1-hexene) is polymerised in the presence of Ziegler-Natta catalyst, the polymer produced is called linear low-density polyethylene.

• The polymer chain contains 1-3 long branches (branches of a-olefin) per 1000 carbon atom. But these branches are of shorter length than those in LDPE.
• For the preparation of film or sheet, LLDPE is mixed with LDPE.

Comparison Between The Properties Of LOPE And HDPE:

Properties Of Polyethylene

1. Polyethylene is chemically inert. It is acid and alkali-resistant.
2. It does not exhibit thermal or electrical conductivity.
3. Low-density polyethylene has a tensile strength of medium value, while high-density polyethylene has a high tensile strength.
4. At ordinary temperatures, polyethylene does not dissolve in any solvent. However, it swells to some extent in contact with benzene, CCl₄, etc.
5. In the presence of heat, oxygen, or sunlight, polythene undergoes an irreversible change in its properties (for example., tensile strength, shape, color, etc.) which is known as aging.
6. The tendency of aging of polythene increases with time.

Uses Of Polyethylene

Uses of low-density polyethylene:

1. It is chemically inert, hard and flexible. This is why it is widely used in the manufacturing of films. These films are used in making carry bags, wrappers, and canal lining to prevent wastage of water in canals and ponds, lamination work, and as an alternative for earthen pots in a nursery.
2. It is also used in the manufacturing of water pipes, water tanks, squeeze bottles, cups, window- nets, buckets, mugs, toys, etc., and as an insulator of electrical wires.
3. Uses Of High-Density Polyethylene: Like low-density polyethylene, it is chemically inert, however, its tensile strength is more than that of low-density polyethylene. This is why it is used in the manufacturing of buckets, dustbins, mugs, bottles, etc.

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Polypropylene(PP)

This is a widely used polymer with the following structure:

Manufacturing Of Polypropylene

Manufacturing Of Polypropylene Monomer: Extremely pure propylene [H2C=CHCH3] is required as the monomer for the production of polypropylene. Propylene is produced by the thermal or catalytic cracking of petroleum hydrocarbons. Propylene is also obtained as a byproduct in petroleum refining.

Manufacturing Of Polypropylene Reaction: The coordination polymerisation (this type of polymerisation proceeds through the formation of coordinate complexes as intermediates) of extremely pure and dry propylene gas at a pressure of about 5-25 atm and a temperature of 60-90°C in the presence of Ziegler-Natta catalyst gives polypropylene.

Properties Of Polypropylene

1. The melting point of polypropylene is 170-175°C.
2. Polypropylene has a relatively low density compared to other polymers and hence is very light in weight.
3. It is resistant to acid and alkali and has no electrical and thermal conductivity.
4. It has a high tensile strength.
5. It has a higher tendency to get oxidised with time as compared to polyethylene.
6. At ordinary temperatures, it does not dissolve in commonly known solvents.

Uses Of Polyvinyl Chloride

1. It is used in the manufacturing of water pipes, water tanks, seat covers, buckets, mugs, radio and television cabinets, etc.
2. It is extensively used as a packaging material.

Polyvinyl Chloride(PVC)

The structural formula of polyvinyl chloride is:

Manufacture Of Polyvinyl Chloride

Manufacture Of Polyvinyl Chloride Monomer: The monomer of polyvinyl chloride is vinyl chloride (H₂C=CHCl). It is produced by the thermal dissociation of ethylene dichloride or by the action of hydrogen chloride on acetylene in the presence of mercuric ions.

Manufacture Of Polyvinyl Chloride Reaction: PVC is produced by the ordinary suspension polymerisation method. In this method, polyvinyl chloride is produced by the free radical polymerisation of vinyl chloride in the presence of a peroxide initiator. The temperature of the reaction is maintained at 50-55°C.

Properties Of Polyvinyl Chloride

1. PVC is hard and durable.
2. It is resistant to water, oils, acids, alkalies, and other chemicals.
3. When subjected to heat and light, it undergoes chemical transformation.

Uses Of Polyvinyl Chloride

Polyvinyl chloride is widely used in buildings, transport and packaging materials, electrical, and electronic devices, and the healthcare industry.

1. PVC sheets are used in roofing and to make water tanks.
2. It is used to make water pipes, tubings, and hoses for corrosive materials.
3. It is used to manufacture electrical wires and cable insulations.

Polytetrafluoroethylene (PTFE) or Teflon: The structural formula of polytetrafluoroethylene is commercial or trade name Teflon.

Manufacture Of Polytetrafluoroethylene

Manufacture Of Polytetrafluoroethylene Monomer: Tetrafluoroethylene (F₂C=CF₂) is the monomer of polytetrafluoroethylene. Tetrafluoroethylene is prepared by removing 2 chlorine atoms from dichloro-tetrafluoroethane (ClF₂C—CF₂Cl) or by thermal decomposition of chlorodifluoromethane (CHClF₂).

Manufacture Of Polytetrafluoroethylene Reaction: Polytetrafluoroethylene is produced by the suspension polymerisation of tetrafluoroethylene in the presence of a peroxide initiator (viz. benzoyl peroxide).

Properties Of Polytetrafluoroethylene

1. Polytetrafluoroethylene is a white, crystalline polymer.
2. It is much denser compared to other polymers.
3. It has very high mechanical strength and is heat resistant.
4. It does not show electrical conductivity.
5. Chemically, it is extremely inert.
6. It is resistant to acids and alkalies and is insoluble in most of the solvents.

Uses Of Polytetrafluoroethylene

1. It is used in the manufacture of glass fibres, transformers, plumbing thread tape, etc.
2. It is used in making pipes and tanks for carrying corrosive substances.
3. It is used in making different laboratory apparatus.
4. It is used in making non-stick cookware.

Polystyrene Or Styron

The structural formula of polystyrene is:

Manufacturing Of Polystyrene

Manufacturing Of Polystyrene Monomer: The monomer of polystyrene is styrene CH=CH₂). Ethylbenzene is first prepared by the action of benzene on ethylene in the presence of an AlCl₃ catalyst. Ethylbenzene further undergoes thermal dissociation to form styrene.

Manufacturing Of Polystyrene Reaction: Styrene undergoes polymerisation in the presence of a peroxide initiator (benzoyl peroxide) to form polystyrene.

Properties Of Polystyrene

1. Polystyrene is a colorless, transparent polymer.
2. It is hard, durable, and brittle.
3. It is resistant to acids, alkalies, and other chemicals.
4. It has a very low water absorption capacity and is suitable for molding.

Uses Of Polystyrene

1. It is used extensively in packaging, especially in the food packaging industry.
2. It is used for coating electrical or electronic appliances like TV or radio cabinets, to give it an excellent finish.
3. It is used in the construction of roofing, sliding panels, plumbing fixtures, and so on.

Polyester: Polyester is a specific category of polymers containing an ester group in their main chain. Polyester is formed by the polycondensation of a dicarboxylic acid and a diol. Two commonly used polyesters are—

1. Polyethylene terephthalate [PET, also called Terylene, Terene, Mylar, and Dacron and
2. Glyptal or Alkyd resin.

Polymer Chemistry Guide

Manufacturing Of Polyethylene Terephthalate(PET)

Manufacturing Of Polyethylene Terephthalate Monomer: Ethylene glycol (HOCH₂—CH₂OH) and terephthalic acid (HOOC—C₆H₄—COOH) are the monomers used in the preparation of PET. In the commercial method of preparation of PET, dimethyl terephthalate is used instead of terephthalic acid.

Manufacturing Of Polyethylene Terephthalate Reactions: Preparation ofPET takes place in two steps:

Step-1: Dimethyl terephthalate reacts with excess ethylene glycol in the presence of a catalyst (antimony trioxide and cobalt acetate) at a temperature of about 150 – 220°C to give bi-(2-hydroxyethyl) terephthalate.

Step 2: In this step, the temperature of the reaction system is raised to 220 -285°C. Here, bis(2 hydroxyethyl) terephthalate undergoes trans-esterification to form polyethylene terephthalate.

Properties of polyethylene terephthalate (PET):

1. PET is a colorless, transparent polymer with a melting point of around 265°C.
2. PET is highly durable and has very high mechanical strength.
3. It is resistant to different chemicals, heat, and abrasion.
4. It has a very low water absorption capacity.

Uses Of Polyethylene Terephthalate (PET):

1. Terylene or dacron is manufactured from PET. Terylene is mainly used to make clothes. It does not absorb water and, hence, dries quickly. It resists wrinkling.
2. Polyethylene terephthalate is used to make water bottles, containers, jars, and various packaging materials. It is also used in the manufacture of magnetic tapes used in recordings.

Manufacturing Of Glyptal Or Alkyd Resin

The polyester resin obtained from polycondensation of polyhydroxy alcohol and dicarboxylic acid is known as an alkyd resin. Glyptal is one such polyester resin.

Manufacturing Of Glyptal Or Alkyd Resin Monomer: Phthalic anhydride and glycerol.

Manufacturing Of Glyptal Or Alkyd Resin Reaction: Phthalic anhydride and glycerol undergo polycondensation to form glyptal or polyglycerylphthalate. It is a cross-linked polymer.

• Two of the three hydroxyl groups of glycerol take part in the polymerisation process.
• The remaining one hangs in the chain. The hanging hydroxyl groups of adjacent monomers combine and form a cross-linked polyester.

Properties And Uses Of Glyptal: Glyptal is brittle and hence does not find too many applications.

Glyptal is prepared by the polycondensation of phthalic anhydride and glycerol along with some vegetable oil(hydrolysis of vegetable oil forms long-chain unsaturated acid) which eventually forms oil-modified alkyd resin. This resin is suitably used in paints and varnishes.

Bakelite

• Phenol-formaldehyde resin is known as bakelite (named after American Chemist Leo Baekeland).
• It is manufactured by carrying out a condensation reaction involving phenol and formaldehyde (mole ratio of phenol to formaldehyde 1:0.7) in the presence of an acid catalyst.
• At the initial stage of the reaction, the reaction of phenol with formaldehyde forms o-/p-hydroxymethyl phenol.
• These then further react with phenol, forming polymer molecules with linear molecular chains. This is called novolac.
• In the molecular chain of novalac, benzene rings are linked with each other through the —CH₂ —group.

Novolac is used in the paint industry. When novolac is heated in the presence of excess formaldehyde, it undergoes crosslinking and forms an infusible solid, called bakelite (resole).

Polymer Chemistry Guide

Properties Of Bakelite

1. It is a thermosetting polymer.
2. It is very hard, insoluble in all solvents, and remains infusible on heating.
3. It is resistant to strong acids but non-resistant to alkali.
4. It is a good insulator of electricity.

Uses Of Bakelite

1. Because of its insulating property, it is used in making electrical equipment such as electrical switches, switchboards, Plugs, etc.
2. As it is water and scratch-resistant, it is used in making combs, phonograph records, computer disks, etc.
3. It is also used in making telephones radio, television cabinets, handles of pressure cooker and saucepan etc.

Melamine-Formaldehyde Resin

• Melamine is added to an alkaline solution(pH = 8.0) of formaldehyde so that the mole ratio of melamine to formaldehyde in the mixture is 1:3.
• On heating the mixture at 80°C, melamine undergoes a condensation reaction with formaldehyde to form melamine-formaldehyde resin.
• At the initial stage of the reaction, methyl melamine is formed, which then converts into melamine-formaldehyde polymers.

Properties Of Melamine-Formaldehyde Resin

1. Its water absorption power is very low.
2. It is very hard and heat resistant.

Properties Of Melamine-Formaldehyde Resin Use: Non-breakable crockery such as discs, cups, etc., are manufactured from this polymer.

Nylon

• Artificial polyamides are called nylon. The eminent scientist Carothers first discovered this fibre. Polymer molecules, containing the amide group(— NHCO —) in their chains, are called polyamides. For the preparation of nylon, dicarboxylic acids, and diamines are used as monomers.
• Polyamides are produced by the condensation of these two monomers. Moreover, it is also produced by condensation reactions of amino acids [RCH(NH₂) — COOH] and ring-opening polymerisation of cyclic monomers containing amide group(for example., lactam type of compounds).

Polymer Chemistry Guide Nylon,6

Manufacture Of Nylon 6

Manufacture Of Nylon 6 Monomer: Caprolactam is used in manufacturing nylon 6.

Manufacture Of Nylon 6 Reactions: When an aqueous solution of caprolactam in the presence of acetic acid as a catalyst is heated at 250°C and at high pressure(12-15 kg/cm² ), nylon 6 is formed.

Properties Of Nylon 6

1. Its melting point is very high(215°C).
2. It is hard and flexible.
3. Its frictional and impact resistance are very high.

Uses Of Nylon 6

It is used in making ropes, tyre cord fabrics, etc.

1. Nylon produced from dicarboxylic acid and diamine is represented by writing the two numbers next to each other. The first number denotes the number of carbon atoms present in the diamine and the second number indicates the number of carbon atoms present in the dicarboxylic acid.
   1. Uses Of Nylon 6 Example: Nylon obtained from hexamethylene diamine (carbon number =6) and adipic acid(carbon number = 6) is written as nylon 6,6. Similarly, nylon produced from hexamethylenediamine(carbon number = 6) and sebacic acid(carbon number = 10) is written as nylon 6,10.
2. Nylon obtained from amino acid or lactam is represented only by a single number, which indicates the number of carbon atoms present in the amino acid or lactam.
   1. Uses Of Nylon 6 Example: Nylon obtained from ω-amino undecanoic acid(11 carbon atoms) is called nylon 11, while nylon produced from caprolactam(6 carbon atoms) is known as nylon6.

Nylon 6,6

Nylon 6,6 is the first synthetic polyamide. Its chemical name is polyhexamethylene adlpamide. It is produced by the condensation polymerisation of adipic acid [HOOC—(CH₂)₄—COOH] and hexamethylenediamine [H₂N—(CH₂)₆—NH₂]. So it is a copolymer.

Manufacture Of Nylon 6,6

Polymer Chemistry Guide

Manufacture Of Nylon 6,6 Monomers: The two monomers used in the manufacture of nylon 6,6 are—

1. Adipic acid and
2. Hexamethylene diamine.

Process Description: For the production of a condensation polymer having high molecular mass, bifunctional monomers are required in the proportion of 1: 1.

• If the mole number of one monomer is either more or less than that of the other, then the molecular mass of the polymer is reduced. Hence, to avoid this problem, the polymerisation reaction is carried out using nylon salt.
• Equimolar quantities of adipic acid and hexamethylene diamine (1:1), react in boiling methanol to give a precipitate of nylon salt (sparingly soluble in methanol) which acts as the true monomer in the polymerisation reaction.

• An aqueous solution of nylon salt (70-75%) is prepared and a small amount of acetic acid (0.5-1 mol%) is added to it
• The acid helps in keeping the molecular mass of the nylon salt at a specific value. The solution is then heated at 200°C, under 20kg/cm² pressure for 2 hours in an autoclave. The reaction is completed by raising the temperature to 280°C.
• As the pressure increases due to the generation of steam during the reaction, the pressure is maintained at 20kg/cm² by releasing some amount of steam.
• After the reaction is over, the pressure in the autoclave is gradually brought down to the atmospheric pressure within 1-2 hours at 280°C.
• Molten nylon is released through a valve at the bottom of the autoclave in an atmosphere of nitrogen and converted into chips by passing it through an extruder.

Properties Of Nylon 6, 6

1. The specific gravity of nylon polymers is generally low, for example., the specific gravity of nylon 6,6 is 1.14.
2. The melting point of nylon 6,6 is 265°C.
3. Nylon is a polar and crystalline polymer.
4. It is tough, pliable, resistant to abrasion, and thermally stable.
5. Due to the presence of hydrogen bonds between the polymeric chains, nylon has a high tensile strength and toughness to carry heavy weights.
6. Due to its polar character and the presence of hydrogen bonds between the polymeric chains, nylon tends to absorb moisture. Nylon 6,6 absorbs nearly 9% of its weight of water.

Uses Of Nylon 6,6

1. As Fibre: It is used in preparing brushes, mosquito nets, sieves, ropes, carpets, and fabrics in the textile industry, fishing nets, etc. It is also used as a cord in tyres which becomes resistant to wear and tear.
2. As Plastic: Due to properties like high tensile strength, toughness, abrasion resistance, thermal stability, etc., nylon 6,6 is used in place of metals for making engineering goods such as automobile bearings, gears, rollers, machinery parts in the textile industry, electrical insulators, etc.

Polymer Chemistry Guide Rubber

Rubber is obtained from nature and can also be produced synthetically.

Natural Rubber

Rubber is produced from the latex of the rubber plant(Hevea brasiliensis). Natural rubber is the cis-polymer of isoprene molecules. A special type of enzyme present in rubber plants produces natural rubber during the polymerisation reaction of isoprene molecules.

In each chain of polyisoprene, 2000-3000 monomer units (isoprene) are present.

Polymer Chemistry Guide

Gutta-percha: Natural rubber is cis-polyisoprene, while trans-polyisoprene is known as gutta-percha, which is also obtained from a natural source.

It is collected from matured leaves of Dichopsis gutta and Palagum gutta plants. At ordinary’ temperatures, gutta-percha is hard and non-elastic but at 100°C, it becomes soft and sticky.

Gutta-percha Uses: It is used in the preparation of golf balls, cables of submarines, furniture, “mourning jewelry” etc.

Disadvantages Of Using Pure Rubber

1. Pure rubber is soft at high temperatures and brittle at low temperatures.
2. It has poor tensile strength and abrasion resistance.
3. It is soft and sticky with a high water absorption capacity.
4. Too much stretching causes permanent deformation of pure rubber.
5. When pure rubber comes in contact with organic solvents such as vegetable oils, gasoline, benzene, chloroform, etc., tends to swell.
6. Pure rubber is attacked by O₂ and O₃, thereby decreasing its stability.

All these defects of natural rubber are removed by vulcanisation. Vulcanised rubber is hard, more elastic, and has higher tensile strength than pure rubber.

Vulcanisation Process

• The vulcanisation process was discovered by Charles Goodyear in 1839.
• He observed that if natural rubber is heated with elementary sulphur, it becomes much stronger, leading to an increase in tensile strength, elastic property, and thermal stability. Its tendency to swell when in contact with organic solvents is also minimised.

Polymer Chemistry Guide

Vulcanisation Process Definition: the process in which thermoplastic rubber is converted into less plastic but more elastic thermosetting rubber is called vulcanisation.

• Previously, the vulcanisation was carried out by heating in the presence of sulphur.
• Later it was also carried out without applying heat in the presence of S₂Cl₂.
• The vulcanisation can also be carried out in the presence of nonsulphur compounds sulphur, for example., organic oximes, organic peroxides, metallic oxides, etc.

Sulphur Vulcanisation: When rubber is heated in the presence of only sulphur, vulcanisation occurs at a slow pace.

• To accelerate the process, organic compounds like thiazole dithiocarbamate, xanthate, guanidine, etc., are added to rubber.
• These are called accelerators. The effectiveness of the accelerators is observed in the presence of specific chemicals. These chemicals are called activators. Generally, metallic oxides (such as ZnO) are used as activators.
• The efficiency of activators is enhanced in the presence of fatty acids (for example., stearic acid). Hence, the important ingredients for effective sulphur vulcanisation are sulphur, organic accelerator, activator, and fatty acid.
• Due to vulcanisation, the isoprene chains in natural rubber are cross-linked by sulphur to give the following structure, along with the liberation of H₂S.

[x=number of sulphur atoms= 1,2,3…,etc.]

In this process, one sulphur atom is cross-linked per 50- 100 monomeric units.

Elasticity Of Rubber Increases On Vulcanisation

• When a stretching force is applied to pure rubber, the polymer chains slip over each other, causing permanent deformation of the rubber.
• The rubber cannot regain its original shape even when the applied force is removed. In vulcanised rubber, the polymer chains are held together by sulphur bridges or crosslinks.
• When a stretching force is applied to vulcanised rubber, the polymer chains of it are straightened out, but they cannot slip over each other because of the cross-linkings.
• When the stretching force is removed, the polymer chains coil up again and the rubber reverts to its original shape.

Properties Of Rubber That Change Its Vulcanisation

1. Vulcanisation increases the hardness and tensile strength of rubber. The tensile strength of pure rubber is nearly 200 kg/cm² and that of vulcanised rubber is as high as 2000 kg/cm².
2. Vulcanisation remarkably increases the resilience or elasticity of rubber. So, by removing stress from the rubber object, it easily regains its previous shape.
3. It remains unaffected by oxygen or ozone.
4. Vulcanised rubber is abrasion-resistant and thermally stable.
5. Vulcanised rubber becomes more resistant to organic solvents and water.
6. Vulcanisation leads to reduced tackiness of rubber.

The Strength Of Vulcanised Rubber Depends On The Quantity Of Sulphur Present In It:

Ebonite: When pure rubber is heated for a prolonged time in the presence of a large quantity of elementary sulphur (40 45 parts per 100 parts of rubber), an extremely hard and strong material is obtained known as ebonite.

• It possesses little or no elastic properties and is widely used as an electrical insulator.
• It is resistant to the action of acids and other chemicals. It is extensively used in the construction of battery boxes, tanks in chemical industries, and so on.

Synthetic Rubbers

Synthetic Rubbers Definition: Synthetic rubbers are commercially prepared polymers with high molecular mass and elasticity and have many similarities with natural rubber.

A brief description of a few synthetic rubbers has been given below.

Butyl Rubber [Isobutylene-isoprene Rubber (IIR)]

• It is a copolymer of isobutylene and isoprene, in which isoprene (2-methyl-1, 3-butadiene) is present in a very small quantity (1-3%).
• Butyl rubber is produced by the cationic polymerisation of isobutylene and isoprene at a very low temperature (-80°C to -105°C ) in the presence of AlCl₃ or BF₃ as a catalyst and methyl chloride as the solvent.

Polymer Chemistry Guide

Butyl Rubber Properties:

1. Butyl rubber has exceptionally low gas and moisture permeability.
2. It is resistant to heat, chemicals, aging, flexing, and abrasion.
3. Butyl rubber is an excellent electrical insulator.

Butyl Rubber Uses:

1. Butyl rubber is extensively used in the inner linings/ tubings of tyres used in cycles and automobiles.
2. It is also used in electrical wires and cable Insulations.

Buna-S Rubber [Styrene-butadiene Rubber (SBR)]: Buna-S is a copolymer of butadiene and styrene. It was marketed with the brand name Buna-S.

• In the name Buna-S Bu’ stands for butadiene, ‘Na’ stands for sodium (Latin: atrium), and ‘S’ stands for styrene.
• The other names of Buna-S are SBR (Styrene-butadiene rubber) and GRS (Government-regulated styrene rubber).
• Buna-S is produced by emulsion polymerisation of the mixture of 75% styrene and 25% butadiene in the presence of initiators (like K₂S₂O₈).

Buna-S Rubber Properties:

1. Buna-S is resistant to abrasion and is highly resilient (elastic).
2. It is easily attacked by oxygen and ozone.
3. It is not resistant to oils and other organic solvents.
4. Like natural rubber, Buna-S can be vulcanised by sulphur or sulphur monochloride (S2C12).

Polymer Chemistry Guide

Buna-S Rubber Uses:

1. Buna-S is primarily used to make automobile tyres.
2. It is widely used to make shoes, heels and soles, hoses, door mats, floor mats, belts, gaskets and even chewing gum.

Buna-N Rubber [Nitrile-butadiene Rubber (NBR)]: It is a copolymer of acrylonitrile (ACN) and butadiene. The mixture of butadiene and acrylonitrile (15-40%) undergoes emulsion polymerisation in the presence of an initiator (a peroxide, like a benzoyl peroxide) to form Buna-N.

Buna-N Rubber Properties: It is highly resistant to heat.0 It is resistant to oils and other organic solvents.

Buna-N Rubber Uses: It is used to make gaskets, conveyor belts, synthetic leather(foam), printer roller, and cable jacketing.

Neoprene Rubber [Chloroprene Rubber(CR)]

Neoprene is the other name of polychloroprene. Chloroprene (2-chlorobutanol-1,3-diene) undergoes emulsion polymerisation in the presence of an initiator to form neoprene.

Neoprene Rubber Properties:

1. Neoprene rubber is highly resistant to abrasion.
2. It has exceptionally high resilience and tensile strength.
3. It is resistant to oil and chemicals and is not attacked by oxygen or ozone.

Neoprene Rubber Uses: It is used to make gaskets, soles, and heels, pipes, hoses, and insulations.

Biodegradable And Non-Biodegradable Polymers

1. Biodegradable Polymers: Polymers that are decomposed by environmental microorganisms to form natural byproducts such as gases (CO2, N2), water, biomass, etc., are known as biodegradable polymers.
   1. Biodegradable Polymers Example: Polylactic acid (PLA), poly-/? -hydroxybutyrate (PHB), polycaprolactone (PCL), polybutylene succinate (PBS), polyethylene adipate (PEA), etc.
2. Non-biodegradable Polymers: Polymers that are not degraded by environmental microorganisms and hence, cannot be converted into simple molecules (such as CO2, H2O, etc.) are called non-biodegradable polymers.
   1. Non-biodegradable Polymers Example: Plastics like polyethylene, polyvinyl chloride, polystyrene, polypropylene etc.
   2. Non-biodegradable polymers are quite resistant to environmental degradation and are responsible for the accumulation of polymeric solid wastes in soil.
   3. These solid wastes remain in undegraded condition for a prolonged period and eventually release toxic chemicals causing soil pollution.

Classification Of Biodegradable Polymers

Based on the origin, it is classified into three main categories:

1. Natural Biodegradable Polymers: These are obtained from natural sources i.e., plants and animals, and are also called biopolymers.
   1. Natural Biodegradable Polymers Example: Starch, cellulose, protein, poly-y -glutamic acid.
2. Synthetic Biodegradable Polymers: These are chemically synthesized.
   1. Synthetic Biodegradable Polymers Example:

Polymer Chemistry Guide

3. Biodegradable Polymer Obtained From Natural Polymer: These are obtained by chemically converting a natural polymer into a biodegradable polymer.

1. Biodegradable Polymer Obtained From Natural Polymer Example: Cellulose acetate, methyl cellulose, carboxy-methyl cellulose.

Biodegradable polymers are enzymatically (intracellular or extracellular) decomposed into simpler molecules by soil bacteria through different chemical reactions (hydrolysis, oxidation, dissociation of the polymeric chain, etc.).

1. Polymer chains having weaker hydrolytic bonds (ester, amide urethane, etc.) are more susceptible to biodegradation, for example., aliphatic polyesters get more easily degraded than aromatic polyesters.
2. Polymers having hydrolytic and weaker flexible bonds are hydrophilic and amorphous. These polymers easily attach to the active sites of enzymes secreted from soil bacteria. So, they are easily biodegradable.
3. Addition or chain polymers (polyethylene, polyvinyl chloride, etc.) are less hydrophilic and crystalline, containing mainly C—C bonds. So they are not acted upon enzymatically by the soil bacteria and hence, are non-biodegradable.

Synthetic Biodegradable Polymers

These polymers are mainly the aliphatic polyesters and aliphatic polyamides. Here is a brief discussion about a few synthetic biodegradable polymers.

Poly-β-hydroxybutyrate-co-β-hydroxy valerate (PHBV): It is formed due to copolymerisation reaction involving 3-hydroxybutyric acid and 3-hydroxy pentanoic add. Monomer units in the polymer chain are held by ester linkages.

Uses of PHBV:

1. It is used in artificial organ transplantation.
2. It is also used in the controlled release of drugs in the human body.

Nylon 2-nylon 6: It is a polyamide, which is formed by polycondensation of glycine and e-aminocaproic add. It is a biodegradable polymer.

Poly(glycolic acid)poly (lactic acid): It is a copolyester, whose commercial name is dextron. It forms on polycondensation involving glycolic acid and lactic acid.

Polymer Chemistry Guide

Poly(glycolic acid)poly (lactic acid) Uses:

1. It is mainly used in making surgical sutures.
2. It is also used in controlled releases of drugs in the human body.

Polylactic acid (PLA): It is a biodegradable polyester, which is obtained from the polycondensation of lactic acid.

Polycaprolactone (PCL): It is a biodegradable polyester, that is obtained from e-caprolactone.

Polycaprolactone Uses:

1. To improve the properties of a resin, it is often mixed with resin as an additive.
2. It is also used in controlled releases of drugs in the human body.

Polymer Chemistry Guide

Class 12 Chemistry Unit 15 Polymers Very Short Questions And Answers

Question 1. Write the names and chemical formulae of the monomers for the following polymers:

Answer:

Question 2.  Which kind of polymer has the same chemical structure for its repeating unit and monomer?
Answer: Polymers formed by addition polymerisation have the same chemical structure for their repeating unit and monomer.

Question 3. Is a homopolymer or copolymer/
Answer: Homopolymer as it is made up of a single monomer (styrene, C₆H₅CH=CH₂).

Polymer Chemistry Guide

Question 4. Is a homopolymer or copolymer?
Answer: Homopolymer as it is formed from a single monomer [H₂N—CH(R)—COOH].

Question 5. Between PVC and dacron, which one is a homopolymer and which one is a copolymer?
Answer: Homopolymer: PVC, Copolymer: Dacron

Question 6. What is the name of the monomer of the following polymer?

Answer: Caprolactam.

Question 7. Name a compound that is used as an initiator in free radical polymerisation.
Answer: Benzoyl peroxide

Question 8. What do the terms ‘Bu’ and ‘S’ in Buna-S indicate?
Answer: Bu: butadiene, S: styrene

Question 9. Which polymer is called myier?
Answer: Polyethylene terephthalate.

Polymer Chemistry Guide

Question 10. What type of polymer does bakelite belong to, thermoplastic or thermosetting?
Answer: Thermosetting.

Question 11. Name a rubber widely used In the manufacturing of car tyres.
Answer:  SBR (Buna-S).

Question 12. Give an example of a monomer that takes part In both free radical and anionic polymerisations.
Answer: Styrene.

Question 13. Name a compound that is used as an initiator in anionic polymerisation.
Answer: Butyllithium (BuLi).

Question 14. What type of polymerisation is known as living polymerisation?
Answer: Anionic polymerisation.

Question 15. Name the monomer of teflon.
Answer: Tetrafluoroethylene (F₂C=CF₂).

Question 16. What is PMMA? Name its monomer.
Answer: PMMA is the name given to polymethyl methacrylate. Its monomer is methyl methacrylate.

Structure:

Question 17. Name the monomer of PAN.
Answer: PAN is polyacrylonitrile. Its monomer is acrylonitrile (H₂C=CH-CN).

Polymer Chemistry Guide

Question 18. Which of the following polymers are synthetic, semisynthetic, and natural polymers? Cellulose acetate, terylene, starch
Answer: Synthetic: terylene, Semi-synthetic: cellulose acetate, Natural: starch.

Question 19. Which of the following are addition and condensation polymers: polypropylene, PET, nylon, PAN.
Answer: Addition Polymer: polypropylene, PAN, Condensation Polymer: PET, nylon.

Question 20. Give an example of a polyamide and a polyester.
Answer: Polyamide: nylon, Polyester: polyethylene terephthalate.

Polymer Chemistry Guide

Question 21. Give an example of each of the thermoplastic and thermosetting polymers.
Answer: Thermoplastic: polyethylene; Thermosetting polymer: unsaturated polyester.

Question 22. Name a copolymer obtained by copolymerisation of three different monomers.
Answer: Acrylonitrile-butadiene-styrene(ABS) copolymer.

Question 23. Why are substances made of polymers lighter than metallic substances?
Answer: The density of polymers is much less than that of metals. Hence, substances made of polymers are much lighter.

Question 24. Which of the following forms a self-polycondensation polymer?

Answer:

Question 25. Give two examples of copolymers.
Answer:

1. Styrene-butadiene (SBR).
2. Styrene-acrylonitrile (SAN).

Question 26. Name two biodegradable polymers used in medicine.
Answer: Polyglycolic acid and polylactic acid are used in surgical sutures.

Polymer Chemistry Guide

Question 27. Name the monomers used in the preparation of glycerol.
Answer: Phthalic anhydride and glycerol.

Question 28. Name the monomer of natural rubber.
Answer: Isoprene (2-methyl-l, 3-butadiene).

Question 29. What is the trade name of trans-polyisoprene?
Answer: Gutta-percha.

Question 30. Which polymer is also known as plexiglass?
Answer: Polymethyl methacrylate (PMMA) is also known as plexiglass.

Question 31. Name the polymers that have the same empirical formulae as that of their monomers.
Answer: Addition polymer

Polymer Chemistry Guide

Question 32. Identify the addition and condensation polymers from the following: polyester, polyacrylonitrile, nylon, and polypropylene.
Answer: Addition polymer: polyacrylonitrile, polypropylene, Condensation polymer: polyester, nylon

Question 33. What is the other name of Teflon?
Answer: Polytetrafluoroethylene (PTFE)

Question 34. Name the polymer that is popularly known as terylene.
Answer: Polyethylene terephthalate

Question 35. Write the name and the formula of a monomer of natural rubber.
Answer: Isoprene,

Question 36. Name the repeating unit of polymethyl methacrylate (PMMA).
Answer:

Polymer Chemistry Guide

Question 37. Name the monomer and chemical formula of protein.
Answer: Amino acid

Question 38. Between long chain and cross-linked polymers, which one has the highest density and melting point?
Answer: Long chain

Question 39. What do you mean by living polymerisation?
Answer: Anionic polymerisation

Question 40. Which is more branched among LDPE and HDPE?
Answer: LDPE

Question 41. Write the monomer of PVC.
Answer: —CH₂—CH(Cl)—

Polymer Chemistry Guide

Question 42. Name the monomers used in the production of glyptal.
Answer: Phthalic anhydride and glycerol

Question 43. Name the monomers of novolac.
Answer:  Phenol and formaldehyde

Question 44. Name a rubber that is used to make tyre tubes.
Answer: Butyl rubber

Question 45. Name a biodegradable and a non-biodegradable polymer.
Answer: Biodegradable: polylactic acid, non-biodegradable: polyethylene

Question 46. Which of the following is a fibre? Nylon, Neoprene, PVC.
Answer: Nylon.

Polymer Chemistry Guide

Question 47. Arrange the following polymers in the increasing order of their intermolecular forces: Terylene, Polythene, Neoprene
Answer: Neoprene < polythene < terylene

Question 48. Classify the following as addition and condensation polymers: Terylene, Bakelite, Polyvinyl chloride, Polythene.
Answer: Addition polymers: Polyvinyl chloride, and polythene. Condensation polymers: Terylene, Bakelite.

Question 49. Is (NH—CHR—CO)_n, a homopolymer or copolymer?
Answer: It is a homopolymer because the repeating structural unit has only one type of monomer unit, i.e., NH₂—CHR—COOH.

Question 50. A natural linear polymer of 2-methyl-l, 3-butadiene becomes hard on treatment with sulphur between 373 to 415 K, and —S—S— bonds are formed between chains. Write the structure of the product of this treatment.
Answer: Vulcanized rubber

Question 51. Identify the type of polymer. —A—A—A—A—A—
Answer: Homopolymer

Polymer Chemistry Guide

Question 52. Identify the type of polymer. —A—B—B—A—A—A—B—A—
Answer: Copolymer

Question 53. Out of chain growth polymerisation and step growth polymerisation, in which type will you place the following?

Answer: addition or chain growth polymerisation;

Question 54. Identify the type of polymer in the following figure.

Answer: Network or cross-linked polymer

Question 55. Identify the polymer given below:

Answer: Polyisoprene or natural rubber;

Question 56. Can an enzyme be called a polymer?
Answer: Enzyme is a protein, hence it is a polymer of amino acid;

Question 57. Can nucleic acids, proteins, and starch be considered as step growth polymers?
Answer: Yes, because the step-growth polymer is a condensation polymer;

Question 58. How is the following resin intermediate prepared and which polymer is formed by this monomer unit?

Answer: Monomer: melamine and formaldehyde. Gives rise to melamine-formaldehyde resin;

Question 59. To have practical applications why are cross-links required in rubber?
Answer: The cross-linkages between the molecular chains of rubber increase it elasticity

Polymer Chemistry Guide

Question 60. Which factor imparts crystalline nature to a polymer like nylon?
Answer: Due to strong intermolecular H-bonding, the polymeric chains remain closely packed which imparts crystalline character.

Question 61. Name the polymers used in laminated sheets and give the name of monomeric units involved in its formation.
Answer: Urea-formaldehyde; the monomer units are formaldehyde.

Question 62. Which type of biomolecules have some structural similarity with synthetic polyamides? What is this similarity?
Answer: Protein. Both of them have amide linkages;

Question 63. Why should the monomers used, in addition, to polymerisation through the free radical pathway be very pure?
Answer: The presence of impurities in the monomers can act as inhibitors and can lead to the termination of the polymerisation reaction.

Question 64. Phenol and formaldehyde undergo condensation to give a polymer (A) which on heating with formaldehyde gives a thermosetting polymer (B). Name the polymers. Write the reactions involved in the formation of (A). What is the structural difference between two polymers?
Answer:

1. Novolac
2. Bakelite.

Polymer Chemistry Guide

Question 65. Which of the following polymers soften on heating and harden on cooling? What are the polymers with this property collectively called? What are the structural similarities between such polymers? Bakelite, urea-formaldehyde resin, polythene, polyvinyl, polystyrene.
Answer: Polythene, polyvinyl, and polystyrene. They are called thermoplastic polymers.

Polymer Chemistry Guide Class 12 Chemistry Unit 15 Polymers Short Questions and Answers

Question 1. Give examples of monomers that take part in free radical, cationic, and anionic polymerisation.
Answer:

1. Free radical Polymerisation: Ethylene(H₂C=CH₂)
2. Cationic Polymerisation: Isobutylene
3. Anionic Polymerisaiton: Acrylonitrile(H₂C=CH₃—CN)

Question 2. What do 6 in nylon 6 and 6 and 10 in nylon 6,10 indicate?
Answer: The number associated with nylon generally indicates the I number of carbon atoms present in the monomer molecule.

1. Nylon-6 is produced from caprolactam, where the number of carbon atoms present = 6.
2. Nylon 6,10 is produced from hexamethylenediamine, which contains 6 carbon atoms, and sebasic acid, which contains 10 carbon atoms.

Question 3.  Name any two monomers that take part In anionic polymerisation. Why is anionic polymerisation also known as living polymerisation? Explain.
Answer: First part: acrylonitrile, styrene.

Question 4. Explain whether homopolymers can be prepared by both addition and condensation polymerisation?
Answer: Yes, homopolymers can be prepared by addition as well as condensation methods of polymerisation.

Polymer Chemistry Guide

Example: Polythene, PVC, PMMA, PAN, and neoprene are condensation homopolymers. Nylon-6 is a long-chain homopolymer.

Question 5. Name the monomer of nylon-6. Mention its uses.
Answer: The monomer of nylon-6 is caprolactam.

Nylon-6 is used to make tyre-chord, ropes, and fabric, and also used as plastics.

Question 6. What is the degree of polymerisation?
Answer: The degree of polymerisation denotes the number of repeating units, present in a molecular chain of a polymer.

• For example,’ n’ is the degree of polymerisation of the polymer .
• Since the chain lengths of the polymer molecules produced in any polymerisation reaction are not identical, the degree of polymerisation is expressed as the average degree of polymerisation.

Question 7. Distinguish between natural and vulcanised rubber.
Answer:

Polymer Chemistry Guide

Question 8. Name the monomer of melamine formaldehyde polymer. Write its uses.
Answer: The monomers of melamine formaldehyde polymer are melamine and formaldehyde.

Polymer Chemistry Guide

This is used in the manufacture of unbreakable utensils.

Question 9. Why is it important to have monomers in their purest form in free radical addition polymerisation?
Answer: Traces of impurities present in the monomers can act as inhibitors and terminate the polymerisation reaction, which results in short-chain polymers. Hence, it is important to have monomers in their purest form in free radical addition polymerisation.

Question 10. Why is bakelite known as a thermosetting polymer?
Answer: Bakelite does not melt on heating and does not get back to its original state on cooling due to extensive crosslinking within the polymer. Hence, bakelite is known as a thermosetting polymer.

Question 11. Identify the following polymers according to their classes.

1. — A — A — A — A — A — A —
2. — A — B — B — A — A — A — B —
3. 

Answer:

1. It is made up of one type of monomer. So, it is a homopolymer.
2. It is made up of two different types of monomers. Hence, it is a copolymer.
3. In this polymer, chains are linked through cross-linking. Hence, it is a network polymer.

Polymer Chemistry Guide

Question 12. What is the role of sulphur in the vulcanisation of natural rubber?
Answer: Vulcanisation of natural rubber forms cross-links between the molecules in the presence of sulphur. This leads to increased hardness and resilience in rubber. Vulcanisation makes it much more abrasion-resistant and thermally stable.

Question 13. Define the term, ‘homopolymerisation’ by giving an example.
Answer: The polymers formed by the polymerisation of only one type of monomer unit are known as homopolymers and the process is known as homopolymerisation.

Example: Formation of polythene:

Question 14. Write the name of monomers used for getting the following polymers:

1. Teflon
2. Buna-N.

Answer:

1. Tetrafluoroethylene;
2. Butadiene and acrylonitrile.

Question 15.

1. What is the role of t-butyl peroxide in the polymerisation of ethene?
2. Arrange the following polymers in the increasing order of their intermolecular forces: polystyrene, terylene, Buna-S, or, Write the mechanism of free radical polymerisation of ethene.

Answer: t-butyl peroxide is used as an initiator for the radial polymerisation of ethene

• Buna-S is an elastomer, terylene is a fibre and polystyrene is a thermoplastic polymer.
• The strength of intermolecular forces in these types of polymers follows the order: elastomer < thermoplastic polymer < fibre.
• Therefore, the intermolecular forces of the given polymers will follow the order: Buna-S < polystyrene < terylene.

Question 16. Shyam went to a grocery shop to purchase some food items. The shopkeeper packed all the items in polythene bags and gave them to Shyam. But, Shyam refused to accept the polythene bags and asked the shopkeeper to pack the items in paper bags. He informed the shopkeeper about the heavy penalty imposed by the government for using polythene bags. The shopkeeper promised that he would use paper bags in the future in place of polythene bags. Answer the following:

1. Write the values (at least two) shown by the Shyam.
2. Why did Shyam refuse to accept the items In polythene bags?

Answer: The values shown by Shyam are environmental protection, public awareness, and social development. Polythene bags are made up of non-biodegradable polymers. So, Shyam refused to accept these bags.

Question 17. Explain the difference between Buna-N and Buna-S.
Answer: Both Buna-N and Buna-S are copolymers. But the monomeric units of Buna-N are 1,3-butadiene and acrylonitrile; whereas I3una-S Is obtained by the copolymerisation of 1,3-butadiene and styrene.

Polymer Chemistry Guide

Question 18. How do you explain the functionality of a monomer?
Answer: Functionality is the total number of bonding sites or functional groups present in a monomer. Example: Functionality of ethene H₂C=CH₂ is 1, whereas 1,3- butadiene is bifunctional, H₂C=CH—CH=CH₂, containing two binding sites.

Question 19. In which classes, the polymers are classified based on molecular forces?
Answer: Based on molecular forces, polymers are classified into the following classes—

1. Elastomers,
2. Fibers,
3. Thermosetting plastics and
4. Thermoplastics.

Question 20. Write the monomers used for getting the following

1. Polymers.
2. Plyvinyl chloride0 Teflon
3. Bakelite.

Answer:

The monomers used for getting the following polymers are

1. Polyvinyl chloride—Vinyl chloride[CH₂=CH—Cl ]
2. Teflon — Tetrafluoroethylene [F₂C=CF₂].
3. 

Question 21. Write the name and structure of one of the common initiators used in free radical addition polymerisation.
Answer: Benzoyl peroxide(BPO) is a common initiator used in free radical addition polymerisation.

Polymer Chemistry Guide

Question 22. How does the presence of double bonds in rubber molecules influence their structure and reactivity?
Answer: Natural rubber is cis-polyisoprene and obtained by 1,4-polymerisation of isoprene units. In this polymer, double bonds are located between C₂ and C₃ of each isoprene unit.

• These ds-double bonds do not allow polymer chains to come closer for effective interactions and hence, intermolecular forces are quite weak.
• As a result, it has a randomly coiled structure and shows elasticity.

Question 23. What are the monomeric repeating units of Nyion-6, and Nylon-6,6?
Answer: The monomeric unit of Nylon-6 is caprolactam. The monomeric unit of Nylon-6,6 is adipic acid and hexamethylenediamine.

Question 24. Write the names and structures of the monomers of the following polymers:

1. Buna-S
2. Buna-N
3. Dacron
4. Neoprene.

Answer: Buna-S: styrene and butadiene.

Polymer Chemistry Guide

Question 25. How Is dacron obtained from ethylene glycol and terephthalic acid?
Answer: Dacron Is obtained by condensation polymerisation of ethylene glycol and terephthalic acid at 420-460K using zinc acetate and antimony oxide as catalysts.

But, dacron Is commercially produced try using dimethyl terephthalate, Instead of terephthalic acid.

Question 26.  What is a biodegradable polymer? Give an example of a biodegradable aliphatic polyester.
Answer: Second part: Poly hydroxybutyric ca-fi -hydroxy valerate (PHBV) is a biodegradable aliphatic polyester.

Question 27. Explain whether cationic or anionic polymerisation takes place in the preparation of acrylonitrile.
Answer: The electronegative — CN group present in acrylonitrile (CH₂=CH—CN) is responsible for the Increased stability of the carbanion.

Since carbanion is formed as an intermediate in both chain initiation and chain propagation, acrylonitrile should be prepared by anionic polymerisation.

Polymer Chemistry Guide

Question 28. Compounds like ice, NaCl, etc., have a sharp melting point. However, polymers do not have a sharp melting point. Give reasons.
Answer: Polymers are formed by the combination of molecules (monomers) of different molecular weights.

• When polymers melt, the smaller molecules with low melting points melt first followed by the heavier molecules.
• Thus, the entire polymer does not melt at a fixed temperature, rather it melts in a temperature range. Hence, polymers do not have a sharp melting point.

Question 29. What do you mean by polymer additive?
Answer: The polymers obtained through polymerisation are virgin and are not suitable for manufacturing.

• Hence, certain substances (like any element or organic compounds) are mixed with these polymers to make them commercially viable. Such substances are known as polymer additives.
• Example: Stabilisers are used to increase the stability of polymers. Plasticisers are used to increase the flexibility of polymers.

Question 30. What do you mean by plasticiser? Give two examples.
Answer: The substances that give flexible polymers with improved activities, when mixed with virgin, rigid polymers are known as plasticisers.

• For instance, polyvinyl chloride (PVC) is a hard, rigid polymer.
• A plasticiser, dioctyl phthalate (DOP) is mixed with PVC to improve its commercial viability.

Example:

1. Tricresyl phosphate is used in polystyrene.
2. Diisooctyl phthalate is used in PVC or polymethyl methacrylate.

Question 31. Why does ris-polyisoprene exhibit elasticity?
Answer: Natural rubber or c/s-polyisoprene does not have a polar group.

• Hence, their chains are linked by weak van der Waals forces. The ds-configurations of the double bond don’t allow the chains to get close to one another.
• This leads to the formation of a coiled structure rather than a long straight chain structure.
• Thus, natural rubber can be stretched like a spring which recoils back when the stretching force is removed, i.e., ds-polyisoprene shows elasticity.

Polymer Chemistry Guide

Class 12 Chemistry Unit 15 PolymersLong Questions And Answers

Question 1. Which of the following polymers are long chains and which of them are cross-linked condensation polymers? Explain.

1. Ethylene glycol
2. Glycerol
3. Terephthalic acid

Answer: Ethylene glycol HO—(CH₂)₂—OH and terephthalic acid (HOOC—C₆H₄ —COOH), each possess two active bifunctional groups.

• Hence, they undergo polycondensation to form a long straight-chain polymer known as polyester.
• Glycerol (HOCH₂—CHOH—CH₂OH) contains three functional groups. Hence, polycondensation of glycerol with terephthalic add forms a network polymer.
• During polycondensation, two —OH groups of glycerol react with the add to form an ester. The remaining —OH groups hanging in the polymer chain form a polyester as a result of the polycondensation.
• Thus, the hanging —OH groups are bonded to the —OH groups of the adjacent polymer chain forming a cross-link, and a network polymer is formed.

Question 2. A natural polymer of 2-methyl-1,3-butadiene when treated with sulphur at 373 K to 415 K, it gets hardened. In the reaction, chains of polymers become connected by —S—S— linkages. Write the structure of the substance formed in the reaction.
Answer: The natural polymer of 2-methyl-1, 3-butadiene is, commonly known as natural rubber.

• When it is treated with sulphur between temperatures 373K to 415K, chains of the polymers become bonded with each other through —S—S— crosslinking.
• This reaction is called vulcanisation of rubber. As a result of this reaction, natural rubber, which is otherwise soft and sticky, becomes hardened.

Polymer Chemistry Guide

Question 3. Arrange the polymers in order of their increasing intermolecular forces:

1. Nylon 6, 6, Buna-S, polyethylene,
2. Nylon 6, neoprene, polyvinyl chloride

Answer:

• Buna-S and neoprene are elastomers. On the other hand, polyethylene, polyvinyl chloride, nylon 6, and nylon 6, 6 are thermoplastic polymers.
• Intermolecular forces of attraction in elastomers are weaker than those in thermoplastic polymers.
• Nylon 6 and nylon 6, 6 are polar. Molecular chains in these two polymers are held by hydrogen bondings.
• Because of this, intermolecular forces of attraction in nylon 6 or nylon 6, 6 are stronger than those in polyethylene or polyvinyl chloride.

Therefore, in the case of

1. The order will be: Buna-S < polyethylene < nylon 6,6 and in the case of
2. It will be neoprene < polyvinyl chloride < nylon 6.

Polymer Chemistry Guide

Question 4. Identify the monomer in the following polymers:

Answer:

The monomers are decanoic acid and hexamethylenediamine.

The monomers are melamine (2,4,6-triamino-1,3,5- triazine) and formaldehyde.

Polymer Chemistry Guide

Question 5. How can you differentiate between addition and condensation polymerisation?
Answer: The addition polymers are formed by the repeated addition of monomer units having double or triple bonds.

1. The condensation polymers are formed by repeated condensation reactions between two different bi-functional or tri-functional monomeric units.
2. In condensation polymerisation, the elimination of small molecules such as water, alcohol, hydrogen chloride, etc. takes place.
3. Addition polymers formed by the polymerisation of a single monomeric species are known as homopolymers, whereas addition polymers obtained from two different monomeric units are termed copolymers.

Examples:

Here, 1 and 2 are examples of addition polymerisation, and 3 is of condensation polymerisation.

Polymer Chemistry Guide

Class 12 Chemistry Unit 15 PolymersMultiple Choice Questions And Answers

Question 1. Silicone oil is obtained from the hydrolysis and polymerisation of—

1. Trimethylchlorosilane and dimethyldichlorosilane
2. Trimethylchlorosilane and methyl trichlorosilane
3. Methyltrichlorosilane and dimethyldichlorosilane
4. Triethylchlorosilane and diethyldichlorosilane

Answer: 1. Trimethylchlorosilane and dimethyldichlorosilane

Question 2. Which is not classified as thermoplastics—

1. Polyethylene
2. Polystyrene
3. Bakelite
4. Neoprene

Answer: Bakelite

Polymer Chemistry Guide

Question 3. Arrange the following monomers in order of decreasing ability to undergo cationic polymerisation—

1. CH₂=CH—C₆H₄(NO₂)
2. CH₂=CH—C₆H₄(CH₃)
3. CH₂=CH—C₆H₄(OCH₃)

1. 1 > 2 > 3
2. 2 > 1 > 3
3. 3 > 2 > 1
4. 1 > 2 > 3

Answer: 3. 3 > 2 > 1

• Electron-releasing groups such as —CH₃, —OCH₃ activate the monomer towards cationic polymerisation because these groups provide stability to the carbocation formed.
• On the other hand, —NO₂ is an electron-withdrawing group. So, it reduces the stability of the carbocation formed. Thus, the correct order is

Question 4. Which of the following polymers of glucose is stored by animals—

1. Cellulose
2. Amylose
3. Amylopectin
4. Glycogen

Answer: 4. Glycogen

Question 5. Which of the following is not a semisynthetic polymer—

1. Cis-polyisoprene
2. Cellulose nitrate
3. Cellulose acetate
4. Vulcanised rubber

Answer: 1. Cis-polyisoprene

Question 6. The commercial name of polyacrylonitrile is _

1. Dacron
2. Orlon (Acrilan)
3. PVC
4. Bakelite

Answer: 2. Orlon (Acrilan)

Polymer Chemistry Guide

Question 7. Which of the following polymer is biodegradable—

Answer: 4

Question 8. In which of the following polymers ethylene glycol Is one of the monomer units—

Answer: 1

Question 9. Which of the following statements is not true about low-density polythene—

1. Tough
2. Hard
3. Poor conductor of electricity
4. Highly branched structure

Answer: 3. Poor conductor of electricity

Polymer Chemistry Guide

7. is a polymer having monomer units—

Answer: 1

Question 10. Which of the following polymers can be formed by using the following monomer unit—

1. Nylon-6,6
2. Nylon 2-nylon 6
3. melamine polymer
4. Nylon-6

Answer: 4. Nylon-6

Question 11. Which of the following polymers, need at least one diene monomer for their preparation—

1. Dacron
2. Buna-S
3. Neoprene
4. Novolac

Answer: 2 and 3

Question 12. Which of the following are characteristics of thermosetting polymers—

1. Heavily branched cross-linked polymers
2. Linear slightly branched long chain molecules
3. Become infusible on molding, so cannot be reused
4. Soften on heating and harden on cooling, can be reused

Answer: 1 and 3

Polymer Chemistry Guide

Question 13. Which of the following polymers are thermoplastic—

1. Teflon
2. Natural rubber
3. Neoprene
4. Polystyrene

Answer: 1 and 4

Polymer Chemistry Guide

Question 14. Which of the following polymers are used as fibre—

1. Polytetrafluoroethylene
2. Polychloroprene
3. Nylon
4. Terylene

Answer: 3 and 4

Question 15. Which of the following are additional polymers—

1. Nylon
2. Melamine formaldehyde resin
3. Orlon
4. Polystyrene

Answer: 3 and 4

Polymer Chemistry Guide

Question 16. Which of the following are condensation polymers—

1. Bakelite
2. Teflon
3. Butyl rubber
4. Melamine formaldehyde resin

Answer: 1 and 4

Question 17. Which of the following monomers form biodegradable polymers—

1. 3-hydroxybutanoic acid + 3-hydroxypentanoic acid
2. Glycine + amino caproic acid
3. Ethylene glycol + phthalic acid
4. Caprolactam

Answer: 1 and 2

Question 18. Which of the following are examples of synthetic rubber—

1. Polychloroprene
2. Polyacrylonitrile
3. Buna-N
4. Cis-polyisoprene

Answer: 1 and 3

Polymer Chemistry Guide

Question 19. Which of the following polymers can have strong intermolecular forces—

1. Nylon
2. Polystyrene
3. Rubber
4. Polyesters

Answer: 1 and 4

Question 20. Which of the following polymers have vinylic monomer units—

1. Acrilan
2. Polystyrene
3. Nylon
4. Teflon

Answer: 1,2 and 4

Question 21. Vulcanisation makes rubber—

1. More elastic
2. Soluble in inorganic solvent
3. Crystalline
4. More stiff

Answer: 1 and 4

Polymer Chemistry Guide

Question 22. Which of the following is a biodegradable polymer—

1. Nylon-2-nylon-6
2. Nylon-6,6
3. Nylon-6
4. Bakelite

Answer: 1. Nylon-2-nylon-6.

Question 23. Which of the following can be considered as the monomer of natural rubber—

1. H₂C=CH—CH=CH₂
2. H₂C=C(CH₃) — CH=CH₂
3. CH₃—CH=CH—CH₃ (trans)
4. CH₃—CH₂—CH=CH₂

Answer: 2. H₂C=C(CH₃) — CH=CH₂

Question 24. Which of the following is an example of thermosetting plastic—

1. Nylon-6
2. Terylene
3. Bakelite
4. Polyethylene

Answer: 3. Bakelite

Question 25. The bond present in cellulose is—

1. 1, 6′ -β-glycosidic bond
2. 1, 4′ -β-glycosidic bond
3. 1,6′ -α-glycosidic bond
4. 1, 4′ -α-glycosidic bond

Answer: 2. 1, 4′ -/? -glycosidic bond

Polymer Chemistry Guide

Question 26. Which of the following polymers contains an ester bond—

1. Nylon
2. Bakelite
3. Terylene
4. PVC

Answer: 3. Terylene

Question 27. Monomer of Teflon is—

1. FClC=CClF
2. Cl₂C=CCl₂
3. F₂C=CF₂
4. FCIC=CF₂

Answer: 3. F₂C=CF₂

Question 28. Neoprene is the polymer of—

1. Vinyl chloride
2. Chloroprene
3. Butadiene
4. Propene

Answer: 2. Chloroprene

Question 29. The biodegradable polymer belonging to the polyamide group is—

1. Dextron
2. Nylon-2-nylon-6
3. Nylon-6,6
4. PHBV

Answer: 2. Nylon-2-nylon-6

Polymer Chemistry Guide

Question 30. Monomer-pair needed to prepare Dacron is—

1. Acrylonitrile and vinyl acetate
2. Terephthalic acid and ethylene glycol
3. Phthalic acid and ethylene glycol
4. Adipic acid and hexamethylene diamine

Answer: 2. Terephthalic acid and ethylene glycol

Question 31. Which of the following is used to prepare paints?

1. Chloroprene
2. Nylon
3. Terylene
4. Glyptal

Answer: 4. Glyptal

Polymer Chemistry Guide

Question 32. Which process helps in the synthesis of polymer from monomer—

1. Hydrolysis of monomer
2. Condensation of monomer molecules
3. Protonation of monomer
4. None of these

Answer: 2. Condensation of monomer molecules

Question 33. Natural rubber is—

1. Polysaccharide
2. Polyamide
3. Polyester
4. Cis-polyisoprene

Answer: 4. Cis-polyisoprene

Question 34. Answer: Which one of the following statements is false—

1. The size of a polymer molecular is 100 or 1000 times larger than a compound molecule
2. Polymer does not have a specific molecular weight
3. Polymers possess a fixed melting point
4. The viscosity of polymer solution is of high values

Question 35. Monomers of Buna-S are—

1. Styrene and butadiene
2. Butadiene
3. Ioprene and butadiene
4. Vinyl chloride and sulphur

Answer: 1. Styrene and butadiene

Polymer Chemistry Guide

Question 36. Which one of the following is not a homopolymer—

1. Teflon
2. SBR
3. PVC
4. Natural rubber

Answer: 2. SBR

Question 37.

1. Homopolymer
2. Copolymer
3. Addition polymer
4. Thermosetting polymer

Answer: 2. Copolymer

Question 38. Which one of the following is a completely fluorinated polymer—

1. Neoprene
2. Teflon
3. Thiocol
4. PVC

Answer: 2. Teflon

Polymer Chemistry Guide

Question 39. Repeating unit of PTTE is—

1. CI₂CH—CH₃
2. F₂C=CF₂
3. F3C—CF₃
4. FCIC=CF₂

Answer: 2. F₂C=CF₂

Question 40. Caprolactam is the monomer of—

1. Nylon-6
2. Terylene
3. Nylon-6,10
4. Nylon-6,6

Answer: 1. Nylon-6

Question 41. Most reactive alkene in cationic polymerisation is—

1. H₂C=CHCH₃
2. H₂C=CF₂
3. H₂C=CHCN
4. H₂C=CHC₆H₅

Answer: 1. H₂C=CHCH₃

Question 42. Which one is used in the vulcanisation of rubber—

1. S₂Cl₂
2. CF₄
3. CI₂F₂
4. C₂F₂

Answer: 1. S₂Cl₂

Polymer Chemistry Guide

Question 43. The monomeric unit present in orlon is—

1. Vinyl cyanide
2. Carolyne
3. Glycol
4. Isoprene

Answer: 1. Vinyl cyanide

Question 44. Which one of the following is a natural fibre—

1. Starch
2. Cellulose
3. Rubber
4. Nylon-6

Answer: 2. Cellulose

Question 45. Which polymer is used as a lubricator and an insulator—

1. SBR
2. PVC
3. PTEE
4. PAN

Answer: 3. PTEE

Question 46. Which one is the initiator in a cationic polymerisation—

1. LiAlH₄
2. HNO₃
3. AICI₃
4. BuLi

Answer: 3. AICI₃

Polymer Chemistry Guide

Question 47. The catalyst used in the polymerisation of olefin is—

1. Zeigler-Natta catalyst
2. Wilkinson catalyst
3. Pd-catalyst
4. Zeolite

Answer: 1. Zeigler-Natta catalyst

Question 48. The compound used in increasing the rigidity of rubber in tyres is—

1. Wax
2. 1,3-butadiene
3. CaC₂
4. Carbon black

Answer: 4. Carbon black

Polymer Chemistry Guide

Question 49. Ebonite is—

1. Natural rubber
2. Synthetic rubber
3. High vulcanised rubber
4. Polypropene

Answer: 3. High vulcanised rubber

Question 50. Which one of the following is not an intermediate in polymerisation—

1. Carbocation
2. Carbanion
3. Free radical
4. Carbene

Answer: 4. Carbene

Polymer Chemistry Guide

Question 51. The full form of PLA is—

1. Polylevulonic acid
2. p-lactic acid
3. Polylactic acid
4. Polylactone acetic acid

Answer: 3. Polylactic acid

Question 52. The monomer of polyethylene is—

1. Ethylene
2. Ethyl amine
3. Ethanoic acid
4. Ethylene glycol

Answer: 1. Ethylene

Question 53. The commercial name of PTTE is—

1. Styrene
2. Glyptal
3. Bakelite
4. Teflon

Answer: 4. Teflon

Question 54. All polymers are macromolecules, but the reverse statement is not true. Which one of the following compounds supports this comment—

1. Polyethylene
2. Polyvinyl chloride
3. Chlorophyll
4. Polystyrene

Answer: 3. Chlorophyll

Question 55. Which one of the following form a polyester network on reaction with terephthalic acid—

1. Ethylene glycol
2. Propylene glycol
3. Glycerol
4. Hydroquinone

Answer: 3. Glycerol

Polymer Chemistry Guide

Question 56. Which one of the following is used for lamination of wood—

1. Phenol-formaldehyde resin
2. Urea-formaldehyde resin
3. Melamine-formaldehyde resin
4. Dacron

Answer: 2. Urea-formaldehyde resin

Question 57. Which one of the following is called neoprene rubber—

Answer: 4

Question 58. Order of intermolecular forces of attraction in the polymers: (1) nylon 6 (2) neoprene and (3) PVC is—

1. 1, 2, 3
2. 2, 1, 3
3. 2, 3, 1
4. 3, 1, 2

Answer: 3. 2, 3, 1

Question 59. Living polymerisation is—

1. Polycondensation polymerisation
2. Free radical polymerisation
3. Cationic polymerisation
4. Anionic polymersation

Answer: 4. Anionic polymersation

Question 60. Which one of the following is elastomer—

1. Polystyrene
2. Neoprene
3. Nylon 6, 6
4. Bakelite

Answer: 2. Neoprene

Polymer Chemistry Guide

Question 61. Which one of the following is the most inert polymer—

1. Terylene
2. Teflon
3. Bakelite
4. Cellulose

Answer: 2. Teflon

Question 62. Strong intermolecular force of attraction like H bonding is present in the polymer—

1. Natural rubber
2. Teflon
3. Nylon-6,6
4. Polystyrene

Answer: 3. Nylon-6,6

Question 63. Which of the following polymers is stored in the liver of animals—

1. Amylose
2. Cellulose
3. Amylopectin
4. Glycogen

Answer: 4. Glycogen

Question 64. Which of the following is a polymer—

1. Carnauba wax
2. Carbowax
3. Beeswax
4. Paraffin wax

Answer: 2. Carbowax

Question 65. Polymer used in bulletproof glass is—

1. PMMA
2. Lexan
3. Nomex
4. Kevlar

Answer: 1. PMMA

Polymer Chemistry Guide

Question 66. The condensation polymer/s is/are—

1. Teflon
2. PET
3. Polystyrene
4. Nylon

Answer: 2. PET

Question 67. The thermoplastic polymer/s is/are—

1. Polyvinyl chloride
2. Bakelite
3. Polypropylene
4. Polyethylene

Answer: 1,3 and 4

Question 68. The two monomers of Buna-S are—

1. Isopropylene
2. Styrene
3. Alkylonitrile
4. Butadiene

Answer: 2 and 4

Question 69. Choose the correct statements—

1. Polymers have sharp melting points
2. Polymer solutions are more viscous
3. Polymers have specific molecular weights
4. Substances made of polymers generally have lightweight

Answer: 2,3 and 4

Polymer Chemistry Guide

Question 70. The polymer obtained by the polycondensation of phenol and formaldehyde is—

1. Novolac
2. Polyester
3. Resole
4. Glyptal

Answer: 1 and 3

Question 71. On vulcanisation, the natural rubber goes through changes in some of its properties like—

1. Decrease in elasticity
2. Increase in resistance to abrasion
3. Decrease in resistance to heat
4. Increase in tensile strength

Answer: 2 and 4

Question 72.

1. Homopolymer
2. Copolymer
3. Condensation polymer
4. Addition polymer

Answer: 1 and 4

Question 73. Vinyl cyanide is used for the manufacture of—

1. Buna-S
2. ABS
3. Buna-N
4. Neoprene

Answer: 2. ABS

Question 74. Which of the following is a polyamide—

1. Protein
2. Dacron
3. Nylon
4. Melamine-formaldehyde resin

Answer: 1 and 3

Polymer Chemistry Guide

Question 75. Nylon 2 – nylon 6 is a biodegradable polymer. The monomers of these polymers are—

1. Glycine
2. Caprolactam
3. Aminocaproic acid
4. Adipic acid

Answer: 1 and 3

Question 76. Which of the following statements are not true regarding gutta-percha and natural rubber–

1. Gutta-percha is an artificial polymer
2. Both are natural
3. Both have the same structure
4. They have different structure

Answer: 2 and 4

Question 77. Which of the following are biodegradable polymers—

1. Dacron
2. Polylactic acid
3. Poly e-caprolactone
4. Nylon 6, 10

Answer: 2 and 3

Polymer Chemistry Guide

Question 78. Which pairs of the following form biodegradable polymer—

Answer: 1 and 4

Polymer Chemistry Guide

Question 79. Which of the following are correctly designated—

1. Polyvinyl chloride: branched polymer
2. Bakelite: network polymer
3. Polypropene: thermoplastic polymer
4. Terylene: thermoplastic polymer

Answer: 1 and 4

Class 12 Chemistry Unit 15 Polymers Match The Following Questions And Answer

Question 1.

Answer: 1-E, 2-C, 3-A, 4-B, 5-D

Polymer Chemistry Guide

Question 2.

Answer: 1-C, 2-A, 3-B, 4-E, 5-D

Question 3.

Answer:  1-B, 2-C, 3-A, 4-E, 5-D

Polymer Chemistry Guide

Question 4.

Answer: 1-D, 2-D, 3-A, 4-E, 5-B, 6-(C;

Question 5.

Answer: 1-D, 2-A, 3-B

Question 6.

Answer: 1-B, 2-(iv), 3-A, 4-D, 5-C

Polymer Chemistry Guide

Question 7.

Answer: 1-F, 2-E, 3-A, 4-C, 5-B, 6-D

Question 8.

Answer:  1-D, 2-A, 3-B, 4-E, 5-C;

Polymer Chemistry Guide

Question 9. Match the following—

1. 1-A; 2-B; 3-C; 4-D
2. 1-B; 2-A; 3-C; 4-D
3. 1-A; 2-B; 3-D; 4-C
4. 1-D; 2-C; 3-A; 4-B

Answer: 1. 1-A; 2-B; 3-C; 4-D

1. Biodegradable polymer →PHBV (3-hydroxybutanoic acid + 3-hydroxypentanoic acid)
2. Bakelite → Phenol + Formaldehyde
3. Neoprene→ 2-chlorobutanol-1,3-diene
4. Glyptal → Phthalic acid + Ethylene glycol

Class 12 Chemistry Unit 15 Polymers Assertion-Reason Type

In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct answer out of the following choices.

1. (A) and (R) both are correct statements but reason does not explain (A).
2. (A) and (R) both are correct statements and (R) explains the (A).
3. Both (A) and (R) are wrong statements.
4. (A) is the correct statement and (R) is the wrong statement.
5. (A) is a wrong statement and (R) is a correct statement.

46. Assertion (A): Rayon is a semi-synthetic polymer and is taken as a better choice than cotton fabric.

Reason (R): Mechanical and aesthetic properties of cellulose can be improved by acetylation.

Answer: 2. (A) and (R) both are correct statements and (R) explains the (A).

47. Assertion (A): Most of the synthetic polymers are not biodegradable.

Reason (R): The polymerisation process induces toxic character in organic molecules.

Answer: 4. (A) is the correct statement and (R) is the wrong statement.

48. Assertion (A): Olefinic monomers undergo addition polymerisation.

Reason (R): Polymerisation of vinyl chloride is initiated by peroxides/persulphates.

Answer: 1. (A) and (R) both are correct statements but reason does not explain (A).

49. Assertion (A): Polyamides are best used as fibres because of their high tensile strength.

Reason (R): Strong intermolecular forces (like hydrogen bonding within polyamides) lead to the close packing of chains and increase the crystalline character, hence, providing high tensile strength to polymers.

Polymer Chemistry Guide

Answer: 2. (A) and (R) both are correct statements and (R) explains the (A).

50. Assertion (A): For making rubber synthetically, isoprene molecules are polymerised.

Reason (R): Neoprene (a polymer of chloroprene) is a synthetic rubber.

Answer: 5. (A) is a wrong statement and (R) is a correct statement.

51. Assertion (A): Network polymers are thermosetting.

Reason (R): Network polymers have high molar mass.

Answer: 1. (A) and (R) both are correct statements but reason does not explain (A).

52. Assertion (A): Polytetrafluoroethylene is used in making non-stick cookware.

Reason (R): Fluorine has the highest electronegativity.

Answer: 1. (A) and (R) both are correct statements but reason does not explain (A).

Class 12 Chemistry Unit 15 Polymers Fill in the blanks

Question 1.____is the monomer of Teflon.
Answer: Tetrafluoroethylene

Question 2. Resole is prepared by the action of phenol and formaldehyde in the presence of____ as a catalyst.
Answer: Alkali

Question 3. The chemical name of natural rubber is_____.
Answer:  Cis-polyisoprene

Question 4. The rubber prepared by the copolymerisation of butadiene and acrylonitrile is known as_____.
Answer: Buna-N

Question 5. ____polymerisation is also known as living polymerisation.
Answer: Anionic

Question 6. Glyptal is a/an____ resin.
Answer: Alkyd

Question 7. ____and____are the monomers of nylon 6,6.
Answer: Hexamethylene diamine and adipic acid

Question 8.  ____polymerisation is used in the preparation of polyvinyl chloride from vinyl chloride.
Answer: Addition or long chain

Question 9. Out of polyvinyl chloride and bakelite,_____ is a thermoplastic polymer.
Answer: Polyvinyl chloride

Question 10. Out of LDPE and HDPE,____has more number of side chains in its polymer chain.
Answer: LDPE

Polymer Chemistry Guide

Question 11. Biodegradable polymers are acted upon by____
Answer: Microorganisms

Class 12 Chemistry Unit 15 Polymers Warm Up Exercise

Question 1. What types of polymers have the same structural and repeating units?
Answer: Chain polymer.

Question 2. Write the formulae of the monomers of the following chain polymers:

Answer:

1. H₂C=CH—Cl
2. H₂C=CHCO₂CH₃
3. H₂C=C(CH₃)₂

Question 3. Among the following polymers, which are chain polymers and which are condensation polymers:

1. Teflon
2. Nylon
3. Polyethylene terephthalate
4. Nylon 6,6.

Answer:

1. Chain polymer
2. Condensation polymer
3. Condensation polymer
4. Condensation polymer

Question 4. Is an enzyme a polymer?
Answer: Enzyme is a protein and protein is the polymer of amino acids. Thus, the enzyme is a polymer.

Polymer Chemistry Guide

Question 5. Can polymers like nucleic acids, proteins, and starch be regarded as step-growth polymers?
Answer:

• Yes, nucleic acids, proteins, and starch can be regarded as step-growth polymers which are condensation polymers.
• A large number of polynucleotides, α-amino acids, and α-D-glucose units combine with the loss of H₂O molecules leading to the formation of nucleic acids, proteins, and starch respectively.

Question 6. What type of initiators are used in the cationic and anionic addition polymerisations?
Answer: Lewis acids are used as initiators in cationic polymerisation whereas alkyl or aryl compounds of alkali metals are used as initiators in anionic polymerisation.

Question 7. Mention the difference between Buna-S and Buna-N.
Answer: Buna-S is a copolymer of styrene (PhCH=CH2) and butadiene(H2C=CH—CH=CH2) whereas Buna-N is a copolymer of butadiene (H2C=CH—CH=CH2) and acrylonitrile(H2C=CH—CN).

Question 8. Write the name and structural formula of the polymer used in making non-stick cookware.
Answer: Teflon: -[F2C—C]n

Question 9. What is the reason for the crystalline structure of nylon?
Answer: Nylons are polyamides as they consist of amide groups (—NHCO—) in their backbone chains.

• As amide groups are highly polar, their presence in polymeric chains leads to the formation of intermolecular hydrogen bonds between adjacent chains, thereby holding the chains together tightly.
• The polymeric chains of nylons are usually’ linear and symmetrical. Because of the strong forces of attraction due to hydrogen bonding between the symmetrical chains of nylons, they are aligned in a regular and ordered arrangement. This makes nylons crystalline.

Polymer Chemistry Guide

Question 10. Which polymer is used in making laminated sheets? What is the name of the monomer of this polymer?
Answer: First part: LDPE. Second part: Ethylene

Question 11. Identify the following as biodegradable and non-biodegradable polymers:

1. Polyvinyl chloride (PVC),
2. Polyhydroxybutyrate (PHB),
3. Polystyrene (PS),
4. Polypropylene (PP),
5. Polylactic acid (PLA),
6. Polyethylene (PE),
7. Protein,
8. Polyglutamic acid.

Answer:

1. Biodegradable polymers:
2. polyhydroxy butyrate(PHB),
3. polylactic acid(PLA),
4. protein,
5. polyglutamic acid.
6. Non-biodegradable polymers:
7. polyvinyl chloride (PVC),
8. polystyrene (PS),
9. polypropylene (PP),
10. polyethylene(PE)

Question 12. Give an example of a polymer that is prepared from a monomer that is prone to attack by microorganisms.
Answer:

Question 13. Give an example of an additive that is blended with a non-biodegradable polymer to produce a biodegradable polymer.
Answer: Starch.