Biodegradable polyesters
4 marks · NormalPolyesters are condensation polymers that are more biodegradable than many addition polymers.
State what is meant by a condensation polymerisation reaction.
With reference to chemical bonding, explain why polyesters can be biodegraded more easily than addition polymers.
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(a) A condensation polymerisation is a reaction where monomers join together forming a polymer and a small molecule, often water, is eliminated each time.
(b) Polyesters have ester linkages in their main chain, which are more reactive than the carbon-carbon bonds in addition polymers. These ester bonds can be broken down (hydrolysed) by water or enzymes, allowing microorganisms to degrade them. Addition polymers do not have these linkages and are much more resistant to breakdown.
Common mistakes: Not mentioning ester bond; Vague reasoning about breakdown
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Marking points
B1 (a) · 1 mark · Defines condensation polymerisation (polymer formed + loss of small molecule, e.g. water).
M1 (b) · 1 mark · Mentions ester bonds or linkages in polyester chains.
A1 (b) · 1 mark · Explains ester bonds are hydrolysable or more reactive.
A2 (b) · 1 mark · Contrasts with addition polymers lacking such reactive bonds, hence less biodegradable.
Worked solution
a) Condensation polymerisation is a reaction where monomers combine to form a polymer, releasing a small molecule like water each time a bond forms.
b) Polyesters contain ester bonds, which can be hydrolysed by water or enzymes in the environment, allowing them to break down. Addition polymers are made of strong carbon-carbon bonds that do not easily break down, making them less biodegradable.