Polymers and Chemistry in Everyday Life
This section covers Polymers and Chemistry in Everyday Life: addition and condensation polymerisation, homopolymers and copolymers, natural and synthetic rubber, biodegradable polymers, drugs, food additives, soaps and detergents. Expect classification and structure–use reasoning.
Core rules
- Addition polymers form without loss of small molecules; condensation polymers form with loss of water, HCl or another small molecule.
- Homopolymers use one monomer; copolymers use two or more. Nylon-6,6 is a condensation copolymer of adipic acid and hexamethylenediamine, linked by amide bonds.
- Natural rubber is cis-polyisoprene; vulcanisation cross-links chains with sulphur.
- Soaps are salts of long-chain fatty acids; detergents are synthetic surfactants and work in hard water because their calcium salts are soluble.
Worked example
A polymer sample has molar mass 1.2 × 10⁵ g mol⁻¹ and is made from a monomer of molar mass 60 g mol⁻¹. Degree of polymerisation = polymer molar mass/monomer molar mass = 1.2 × 10⁵/60 = 2000. This means about 2000 monomer units are joined in the average chain. The value is an average because polymer samples are polydisperse.
Traps
Do not call nylon-6,6 an addition polymer; do not confuse homopolymer with copolymer; remember that natural rubber is cis, not trans; do not say soaps work in hard water; classify drugs by action, not by a random example.