Polymers and Plastics

Correct answer. PA6 (nylon 6) is an amorphous polymer, which is made from the polymerisation of caprolactam, not from hexamethylenediamine and anthranilic acid. A model from Solvay industries and Trogamid from Evonik Industries are semi-aromatic polyamides and are made from the polymerisation of hexamethylenediamine and terephthalic acid. Hence, both Q and R are false.

Correct answer. Both Kevlar and Twaron are the registered trademark for para-aramid synthetic fibres, related to other aramids such as Nomex and Technora. Developed by Stephanie Kwolek at DuPont in 1965, Kevlar was first commercially used in the early 1970s as a replacement for steel in racing tires. Kevlar is used in modern times to make modern drumheads that withstand high impact, tyre making and underwater applications, etc. Nomex is the registered trademark for meta-aramid synthetic fibre.

Correct answer. Neoprene is a synthetic rubber and is prepared by the polymerisation of chloroprene as monomer unit.

Correct answer. Terylene (polyester) is a synthetic fibre, which is made from the condensation of ethylene glycol and dimethyl terephthalate.

Correct answer. A large number of polymer applications in different fields depend on their unique mechanical properties like tensile strength, elasticity, toughness, etc. These mechanical properties are governed by intermolecular forces such as van der Waals forces and hydrogen bonds present in the polymer. These forces also bind the polymer chains. Under this category, the polymers are classified into the following four subgroups on the basis of magnitude of intermolecular forces present in them - elastomer, fibre, thermoplastic and thermosetting. Elastomers are rubber–like solids with elastic properties. In these elastomeric polymers, the polymer chains are held together by the weakest intermolecular forces. These weak binding forces permit the polymer to be stretched. A few ‘crosslinks’ are introduced in between the chains, which help the polymer to retract to its original position after the force is released as in vulcanised rubber. Examples are buna S, buna N, neoprene, bromobutyl, Viton (a brand of synthetic rubber and fluoropolymer elastomer commonly used in O-rings and other molded or extruded goods), etc.

Correct answer. Cellulose derivatives such as cellulose acetate (rayon) and cellulose nitrate, etc. are the usual examples of this subcategory.

Correct answer. Cellulose is a homopolymer of glucose as a monomer unit. Insulin is a homopolymer of fructose as a monomer unit and Glyptal is a copolymer of ethylene glycol and phthalic acid. Bakelite is a condensation polymer (copolymer) of phenol and formaldehyde. Hence, statements P and S are incorrect.

Correct answer. Polyetherimide (PEI) is an amorphous, amber-to-transparent thermoplastic, which is made from the polymerisation of etherimide.

Correct answer. Poly methyl methacrylate (PMMA) is produced by the homopolymerisation of methyl methacrylate.

Correct answer. Synthetic polymers are human-made polymers. From the utility point of view, they can be classified into four main categories: thermoplastics, thermosets, elastomers and synthetic fibres. An elastomer is a polymer with viscoelasticity (having both viscosity and elasticity) and very weak intermolecular forces. For example, polychloroprene, neoprene, baypren, elastolefin, etc.

Terylene (polyester) is the condensation polymer of ethylene glycol and dimethyl terephthalate. Nylon 66 is the condensation polymer of hexamethylenediamine and adipic acid. Perspex (polymethyl methacrylate) is prepared by the polymerisation of methyl methacrylate. Polyvinyl chloride (PVC) is formed by the polymerisation of vinyl chloride.

Hence, the correct answer using the codes is P - 3, Q - 4, R - 1, S - 2.

Thermoplastics are characterized by weak Van der Waals forces between polymer chains (allowing melting and reshaping), the ability to melt upon heating, and formation via addition polymerization. They have HIGH molecular weights (typically 10,000-1,000,000 g/mol), not low molecular weights - low molecular weight compounds are usually small molecules or oligomers.

Thermoset plastics (vulcanized rubber, melamine, bakelite) undergo irreversible curing and cannot be remelted. Polystyrene is a THERMOPLASTIC - it softens upon heating and can be reshaped multiple times, making it the correct answer as 'not an example of thermoset'.

Vulcanized rubber is a thermoset polymer that does NOT melt upon heating, is highly resistant to chemical attack, and is insoluble. However, vulcanization creates STRONG covalent cross-links (sulfur bridges) between polymer chains, not weak covalent bonds. This cross-linking is what gives it its thermoset properties.

This statement is incorrect because plastics are generally LESS expensive than metals. Plastics are light in weight, highly durable, and resistant to corrosion - these are all correct properties. The cost advantage is one of the main reasons plastics have replaced metals in many applications.