JEE Chemistry Polymers MCQs Set 11

Answer: (a) cis-polyisoprene

Explanation:
1. Semisynthetic polymers are natural polymers chemically modified.
2. Cellulose nitrate, cellulose acetate and vulcanised rubber are modified natural polymers.
3. cis-Polyisoprene is natural rubber itself, a natural polymer.

Teacher's Note:
1. Vulcanisation (cross-linking natural rubber with sulphur) makes it semisynthetic.

Answer: (b) Orlon (acrilan)

Explanation:
1. Addition polymerisation of acrylonitrile gives polyacrylonitrile, sold as Orlon or acrilan.
2. Dacron is polyester and Bakelite is phenol-formaldehyde resin.

Teacher's Note:
1. Orlon is used as a substitute for wool.

Answer: (c) PHBV (poly-3-hydroxybutyrate-co-3-hydroxyvalerate)

Explanation:
1. PHBV is an aliphatic polyester that is broken down by microorganisms.
2. Polychloroprene, nitrile rubber and nylon-6,6 are not readily biodegradable.

Teacher's Note:
1. PHBV is used in packaging, orthopaedic devices and controlled drug release.

Answer: (a) polyethylene terephthalate (Dacron)

Explanation:
1. Dacron is formed by condensation of ethylene glycol with terephthalic acid.
2. Polythene is from ethene, SBR from styrene and butadiene, and PHBV from hydroxy acids.

Teacher's Note:
1. Dacron is also written as terylene.

Answer: (b) Hard

Explanation:
1. LDPE has a highly branched structure, so chains pack loosely, giving a tough, flexible, low-melting plastic that is a poor conductor of electricity.
2. It is not hard; hardness belongs to high density polythene (HDPE).

Teacher's Note:
1. Branching lowers density and rigidity.

Answer: (a) 2-methylpropene

Explanation:
1. The repeat unit \(\ce{-CH2-C(CH3)2-}\) comes from the monomer \(\ce{CH2=C(CH3)2}\), 2-methylpropene (isobutylene).
2. The polymer is polyisobutylene (butyl rubber is a copolymer with isoprene).

Teacher's Note:
1. Break the chain into repeat units of two carbons from the double bond.

Answer: (d) nylon-6

Explanation:
1. Caprolactam is heated with a little water at 530-540 K; the ring opens and polymerises to nylon-6.

Teacher's Note:
1. Nylon-6 is made from a single monomer; nylon-6,6 needs two.

Answer: (a) Dacron

Explanation:
1. Dacron is formed by condensation of terephthalic acid and ethylene glycol with the loss of water.
2. Neoprene and Teflon are addition polymers, and acrylonitrile is a monomer.

Teacher's Note:
1. Condensation polymerisation eliminates small molecules like water or HCl.

Answer: (c) \(\ce{AlCl3}\)

Explanation:
1. Cationic polymerisation is started by Lewis acids such as \(\ce{AlCl3}\) (with a trace of water) or \(\ce{BF3}\), which generate a carbocation.
2. BuLi is an anionic initiator, and \(\ce{LiAlH4}\) is a reducing agent.

Teacher's Note:
1. Cationic initiators are electron-pair acceptors; anionic initiators are strong bases.

Answer: (c) HCHO

Explanation:
1. Phenol condenses with formaldehyde in the presence of an acid or base to form hydroxymethylphenols and then a cross-linked network, Bakelite.

Teacher's Note:
1. Phenol-formaldehyde resin is a thermosetting plastic used for switches and handles.

Answer: (b) Nylon-6,6

Explanation:
1. Nylon-6,6 has amide linkages (N-H and C=O) that form strong hydrogen bonds between chains, which gives high tensile strength (a fibre).
2. Teflon, polystyrene and natural rubber have only weak van der Waals forces.

Teacher's Note:
1. Fibres have strong forces such as hydrogen bonding; elastomers have weak forces.

Answer: (c) acrylonitrile (\(\ce{CH2=CHCN}\)) and buta-1,3-diene

Explanation:
1. Buna-N (nitrile rubber) is obtained by copolymerisation of buta-1,3-diene and acrylonitrile (N stands for nitrile).
2. Buna-S uses styrene and neoprene uses chloroprene.

Teacher's Note:
1. Buna-N is resistant to oil and petrol.

Answer: (b) Polytetrafluoroethylene

Explanation:
1. Teflon (PTFE) has very low surface energy and is chemically inert, so food does not stick to it.

Teacher's Note:
1. PTFE is made by free radical polymerisation of tetrafluoroethene under pressure.

Answer: (c) Teflon

Explanation:
1. Teflon is polytetrafluoroethylene, \(\ce{-(CF2-CF2)n-}\), with fluorine on every carbon.
2. PVC contains chlorine, Thiokol is a polysulphide and neoprene contains chlorine.

Teacher's Note:
1. Teflon is stable up to about 500 K.

Answer: (c) Nylon-66

Explanation:
1. Nylon-66 is formed by amide linkages between hexamethylenediamine and adipic acid.
2. Terylene is a polyester, Bakelite is a phenolic resin and Teflon is a fluoropolymer.

Teacher's Note:
1. Polyamides contain the repeating -CO-NH- group.

Answer: (c) polyamide polymer

Explanation:
1. Nylon fibres (nylon-6 and nylon-66) contain amide linkages, so they are polyamides.

Teacher's Note:
1. Silk and wool are natural polyamides (proteins).

Answer: (d) phenol-formaldehyde resin (Bakelite)

Explanation:
1. Thermosetting polymers form a cross-linked network on heating and cannot be remelted.
2. Bakelite is the standard example; PVC is thermoplastic, nylon-6,6 is a fibre and polychloroprene is an elastomer.

Teacher's Note:
1. Thermoplastics soften on heating; thermosets set permanently.

Answer: (c) terephthalic acid and ethylene glycol

Explanation:
1. Dacron (terylene) is formed by condensation of terephthalic acid (benzene-1,4-dicarboxylic acid) with ethylene glycol at 420-460 K with zinc acetate/antimony trioxide.

Teacher's Note:
1. A polyester needs a diacid and a diol.

Answer: (d) Neoprene

Explanation:
1. Melamine polymer, glyptal and Dacron are formed with elimination of small molecules (water).
2. Neoprene is formed by addition polymerisation of chloroprene.

Teacher's Note:
1. Glyptal is a polyester of glycerol and phthalic acid.

Answer: (b) Nylon-6,6 is an example of an elastomer

Explanation:
1. Rayon (artificial silk) is regenerated cellulose, natural rubber is polyisoprene, and starch and cellulose are polymers of glucose.
2. Nylon-6,6 is a fibre (strong hydrogen bonding), not an elastomer.

Teacher's Note:
1. Nylon-6,6 is a fibre; natural rubber and neoprene are elastomers.

Answer: (b) glycine and 6-aminohexanoic acid

Explanation:
1. Glycine and 6-aminohexanoic acid (aminocaproic acid) condense to nylon-2-nylon-6, a biodegradable polyamide.
2. The other combinations give non-biodegradable Buna-N, Dacron and Buna-S.

Teacher's Note:
1. Nylon-2-nylon-6 is a biodegradable copolymer of glycine and aminocaproic acid.

Answer: (a) \(\ce{-[CH2-C(Cl)=CH-CH2]n-}\)

Explanation:
1. Neoprene is polychloroprene, made from 2-chlorobuta-1,3-diene: \(\ce{-[CH2-C(Cl)=CH-CH2]n-}\).
2. (b) is PVC, (c) is polyacrylonitrile and (d) is polystyrene.

Teacher's Note:
1. Neoprene is resistant to oil and is used for conveyor belts and gaskets.

Answer: (b) copolymer

Explanation:
1. Nylon-6,6 is made from two different monomers, hexamethylenediamine and adipic acid, so it is a (condensation) copolymer.

Teacher's Note:
1. Homopolymers have one type of monomer, copolymers have two or more.

Answer: (c) Polystyrene

Explanation:
1. Chain-growth polymers form by successive addition of monomers (usually unsaturated) to an active centre.
2. Polystyrene is made by this route.
3. Starch, nucleic acids and proteins are condensation (step-growth) polymers of their monomers.

Teacher's Note:
1. Addition polymers are chain-growth polymers.