Polymer Science

Step 1: Understanding crystallinity in polymers.
Crystalline polymers have regularly arranged chains that pack closely, leading to ordered regions. Strong intermolecular forces favor crystallinity.
Step 2: Structure of Nylon 66.
Nylon 66 contains repeating amide groups (–CONH–) that form strong hydrogen bonds between polymer chains, allowing them to align and crystallize efficiently.
Step 3: Analysis of options.
(A) Polybutadiene: Mostly amorphous elastomer.
(B) Nylon 66: Correct — Highly crystalline due to hydrogen bonding.
(C) Cis polyisoprene: Natural rubber, largely amorphous.
(D) Polychloroprene: Elastomer with low crystallinity.
Step 4: Conclusion.
Nylon 66 is expected to be a crystalline polymer, hence option (B) is correct.

Step 1: Understanding glass transition temperature.
Glass transition temperature (T_g) depends on chain rigidity, bulky side groups, and intermolecular interactions. More rigid chains show higher T_g.
Step 2: Structural comparison.
Polystyrene contains bulky phenyl groups attached to the polymer backbone, which restrict molecular motion and increase chain stiffness compared to other polymers listed.
Step 3: Analysis of options.
(A) Polyethylene: Flexible chains with very low T_g.
(B) Polypropylene: Slightly higher T_g than polyethylene.
(C) Cis polyisoprene: Elastomer with low T_g.
(D) Polystyrene: Correct — Bulky phenyl groups lead to highest T_g.
Step 4: Conclusion.
Polystyrene has the highest glass transition temperature among the given polymers, so option (D) is correct.

Step 1: Understanding fibre-forming polymers.
Fibre-forming polymers are polymers that possess high tensile strength, elasticity, and the ability to be drawn into fibres. They usually have strong intermolecular forces like hydrogen bonding.
Step 2: Structural requirement.
Polyamides contain amide linkages (–CONH–) that enable hydrogen bonding between polymer chains, providing strength and fibre-forming capability.
Step 3: Analysis of options.
(A) Polyisoprene: Mainly used in rubber, not fibre formation.
(B) Polyamides: Correct — Nylon is a polyamide and a well-known fibre.
(C) Polyethers: Generally flexible polymers, not fibre-forming.
(D) Polysulfides: Used as elastomers and sealants.
Step 4: Conclusion.
Polyamides are fibre-forming polymers, therefore option (B) is correct.

Step 1: Understanding Buna polymers.
Buna rubbers are synthetic rubbers prepared by copolymerization of butadiene with other monomers. The name “Buna” comes from butadiene and sodium (Na), used as a catalyst.
Step 2: Composition of Buna N.
Buna N, also known as nitrile rubber, is produced by copolymerizing butadiene with acrylonitrile. This composition gives the rubber oil and chemical resistance.
Step 3: Analysis of options.
(A) Butadiene & Acrylonitrile: Correct — This combination forms Buna N.
(B) Butadiene & Styrene: Forms Buna S (SBR rubber).
(C) Butadiene & Isoprene: Not Buna N.
(D) Butadiene & Ethylene: Not used for Buna rubbers.
Step 4: Conclusion.
Buna N is a copolymer of butadiene and acrylonitrile, hence option (A) is correct.

Step 1: Understanding thermoplastics.
Thermoplastics are polymers that soften when heated and harden upon cooling. This process is reversible, allowing thermoplastics to be reshaped multiple times without chemical change.
Step 2: Classification of given materials.
Bakelite, ebonite, and vulcanized rubber are thermosetting polymers. Once set, they cannot be reshaped on heating due to extensive cross-linking. Polycarbonate, however, is a linear polymer with little cross-linking.
Step 3: Analysis of options.
(A) Bakelite: A thermosetting plastic, not thermoplastic.
(B) Polycarbonate: Correct — It softens on heating and can be reshaped.
(C) Ebonite: A hard form of vulcanized rubber, thermosetting in nature.
(D) Vulcanized: Vulcanized rubber is thermosetting.
Step 4: Conclusion.
Polycarbonate is a thermoplastic polymer, hence option (B) is correct.