Synthetic Polymers
6 marks · NormalRead the text and answer the questions that follow.
A city council is deciding whether to promote the use of polyesters in place of traditional addition polymers for packaging. They want to consider both environmental impact and chemical properties.
Explain why many addition polymers are considered non-biodegradable.
Describe the process by which polyesters are formed and how this is different from addition polymerisation.
Suggest and explain one environmental benefit of using some polyesters instead of addition polymers for products that may be discarded into the environment.
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(a) Addition polymers are considered non-biodegradable because their strong covalent bonds make them chemically inert, so they are not broken down by bacteria or natural processes.
(b) Polyesters form by condensation polymerisation, where a diol and a dicarboxylic acid join together with the loss of water, forming ester links between units. This is different from addition polymerisation where only one monomer type is used and no small molecule is lost.
(c) Some polyesters are biodegradable, meaning bacteria and other living things can break them down, so less plastic stays in landfill or the environment for long periods. This reduces persistent pollution compared to addition polymers which do not biodegrade.
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Marking points
B1 (a) · 1 mark · Mentions strong covalent bonds/inertness of addition polymers.
B2 (a) · 1 mark · Mentions that addition polymers are not broken down by bacteria/natural processes.
B3 (b) · 1 mark · Correctly describes condensation polymerisation of polyesters (diol + dicarboxylic acid + loss of water/ester link).
B4 (b) · 1 mark · Notes a difference: addition polymerisation uses one monomer type and no small molecule is lost.
B5 (c) · 1 mark · Correctly identifies that some polyesters are biodegradable or easier to break down.
B6 (c) · 1 mark · Gives an explanation relating this to reduced pollution or easier disposal.
Worked solution
a) Addition polymers are made with very stable, strong covalent bonds making them chemically inert. Because of this, bacteria and natural processes cannot break them down, so they are non-biodegradable.
b) Polyesters are formed by condensation polymerisation: a dicarboxylic acid and a diol react together, losing water molecules to form ester links, joining monomers into long chains. Unlike addition polymerisation, which joins unsaturated monomers and wastes nothing, condensation polymerisation always eliminates a small molecule like water and usually involves two types of monomer.
c) Some polyesters are biodegradable, so bacteria and other decomposers can break them down. This means less waste remains in the environment, reducing plastic pollution compared to addition polymers which do not biodegrade.