JEE Chemistry Polymers MCQs Set 22

Answer: (d) Phenol-formaldehyde resin

Explanation:
1. Proteins, polysaccharides and cotton (cellulose) occur in nature.
2. Phenol-formaldehyde resin (Bakelite) is made in industry from phenol and methanal.

Teacher's Note:
1. Natural polymers are obtained from plants and animals.

Answer: (d) Terylene

Explanation:
1. Terylene (Dacron) is a polyester made from ethylene glycol and terephthalic acid. The rest are natural biopolymers.

Teacher's Note:
1. Terylene is a polyester fibre.

Answer: (b) Nylon-6,6

Explanation:
1. Nylon-6,6 has strong hydrogen bonding between chains, giving high tensile strength and fibre character. Rubber is an elastomer, PVC a thermoplastic and Bakelite a thermosetting plastic.

Teacher's Note:
1. Fibres have strong intermolecular forces.

Answer: (d) Proteins

Explanation:
1. Proteins are natural polyamides of amino acids. Rayon is semi-synthetic and the other two are synthetic.

Teacher's Note:
1. Rayon is regenerated cellulose.

Answer: (d) Bakelite

Explanation:
1. Bakelite is cross-linked, becomes infusible and insoluble on heating in a mould and cannot be softened again.

Teacher's Note:
1. Thermosetting polymers cannot be remoulded.

Answer: (c) Egg albumin

Explanation:
1. Egg albumin is a protein, i.e. a polymer of amino acids.

Teacher's Note:
1. Proteins are natural biopolymers.

Answer: (d) Teflon

Explanation:
1. Teflon is formed by free-radical addition polymerisation of tetrafluoroethylene. Nylon, Bakelite and Terylene are step-growth (condensation) polymers.

Teacher's Note:
1. Alkene monomers give addition polymers.

Answer: (c) Polyester

Explanation:
1. Polyesters are formed by condensation of a diol with a diacid with loss of water. The other three come from alkene monomers.

Teacher's Note:
1. Condensation polymers eliminate small molecules.

Answer: (a) Adipic acid and hexamethylenediamine

Explanation:
1. Nylon-6,6 is formed from adipic acid (6 carbons) and hexamethylenediamine (6 carbons), eliminating water and forming amide links.

Teacher's Note:
1. The two numbers in the name give the carbons of the two monomers.

Answer: (b) Hydrogen bonding

Explanation:
1. Hydrogen bonds form between the N-H of one chain and the C=O of another chain.

Teacher's Note:
1. Amide groups give strong hydrogen bonding.

Answer: (b) Copolymerisation

Explanation:
1. A polymer made of two or more different monomers is a copolymer, for example Buna-S.

Teacher's Note:
1. Co means together.

Answer: (b) A condensation polymer with a benzene ring in every repeating unit

Explanation:
1. Terylene is a polyester of ethylene glycol and terephthalic acid, so each repeat unit contains a benzene ring and two ester links, with no nitrogen.

Teacher's Note:
1. Terylene is a polyester.

Answer: (b) Dacron

Explanation:
1. Dacron contains the ester group -CO-O- formed between the diol and the diacid.

Teacher's Note:
1. Polyesters have ester links.

Answer: (d) Natural rubber

Explanation:
1. Wool and leather are proteins and nylon is a synthetic polyamide. Natural rubber is a polymer of isoprene and has no amide group.

Teacher's Note:
1. Polyamides contain -CO-NH- links.

Answer: (a) A cation

Explanation:
1. Isobutene has two electron-donating methyl groups, which stabilise the carbocation formed in cationic polymerisation.

Teacher's Note:
1. Electron-donating groups favour cationic polymerisation.

Answer: (d) Condensation polymerisation

Explanation:
1. Condensation polymerisation proceeds by reactions between functional groups of the monomers, so no special initiator is needed.

Teacher's Note:
1. Chain-growth reactions need initiators.

Answer: (a) Ziegler-Natta catalyst

Explanation:
1. Ziegler-Natta catalyst, \( \ce{TiCl4} \) with \( \ce{Al(C2H5)3} \), gives stereoregular polymers at low pressure.

Teacher's Note:
1. TiCl4 plus triethylaluminium.

Answer: (c) Isoprene (2-methylbuta-1,3-diene)

Explanation:
1. Natural rubber is cis-1,4-polyisoprene.

Teacher's Note:
1. Isoprene is C5H8.

Answer: (b) Vulcanisation

Explanation:
1. Vulcanisation introduces sulphur cross-links between polymer chains, increasing tensile strength, elasticity and resistance to abrasion.

Teacher's Note:
1. Goodyear discovered vulcanisation.

Answer: (a) -S-S- bonds (sulphur bridges)

Explanation:
1. Sulphur forms disulphide-type bridges at the reactive allylic positions of neighbouring chains.

Teacher's Note:
1. Cross-links stop chains sliding past one another.

Answer: (c) Highly vulcanised rubber

Explanation:
1. Heating rubber with 30 to 50% sulphur gives hard, brittle ebonite.

Teacher's Note:
1. More sulphur gives harder rubber.

Answer: (a) Styrene and 1,3-butadiene

Explanation:
1. Buna-S (styrene butadiene rubber) is made from 1,3-butadiene and styrene with sodium as catalyst.

Teacher's Note:
1. Bu from butadiene, na from sodium, S from styrene.

Answer: (b) Greater than 1

Explanation:
1. PDI = Mw/Mn = 40000/30000 = 1.33, which is greater than 1.

Teacher's Note:
1. PDI is always at least 1.

Answer: (b) 20800

Explanation:
1. The repeating unit is \( \ce{C8H8} \), mass 104.
2. Molecular mass = 200 x 104 = 20800.

Teacher's Note:
1. Styrene is C6H5CH=CH2.

Answer: (a) \( \sum N_iM_i^2 / \sum N_iM_i \)

Explanation:
1. Mw weights each molecule by its mass: Mw = (sum of Ni Mi squared)/(sum of Ni Mi).
2. Mn = (sum Ni Mi)/(sum Ni).

Teacher's Note:
1. Mw is the mass-weighted and Mn the number-weighted average.

Answer: (b) Mw is greater than Mn

Explanation:
1. Synthetic polymers contain chains of different lengths, so Mw > Mn and PDI > 1. Only a monodisperse polymer has Mw = Mn.

Teacher's Note:
1. Heavier chains pull Mw up.