Synthetic Polymers
7 marks · HardMany artificial polymers have useful properties but create environmental concerns. Answer the following questions about their preparation and degradation.
Describe how addition polymers such as poly(chloroethene) are prepared from their monomers, including the conditions needed.
State and explain one main reason why addition polymers like poly(chloroethene) are not easily biodegradable.
Explain why polyesters such as polylactic acid (PLA) are considered more biodegradable than addition polymers.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Addition polymers like poly(chloroethene) are made by heating the monomer (chloroethene) under high pressure with an initiator. The C=C double bonds open up to form long chains. · must show high pressure, initiator, opening of C=C double bond, long polymer chains
(b) Addition polymers are not biodegradable because they are chemically unreactive (inert) and do not contain reactive groups that can be broken down by microorganisms or bacteria. · must show inert, lack of reactive groups, not broken down by microorganisms
(c) Polyesters like PLA have ester linkages, which can be hydrolysed by water and enzymes produced by microorganisms, allowing the polymer to break down. Addition polymers do not have these linkages, so cannot be easily degraded. · must show ester bonds, hydrolysed by water/enzymes, microorganisms break down, contrast with addition polymers
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Marking points
M1 (a) · 1 mark · States correct conditions for polymerisation: high pressure and initiator
M2 (a) · 1 mark · Describes that monomers join by addition across C=C to form long chains
A1 (b) · 1 mark · States that addition polymers are non-biodegradable due to inertness
A2 (b) · 1 mark · Explains lack of reactive groups for microorganism attack
B1 (c) · 2 marks · Explains that ester bonds can be broken by hydrolysis; microorganisms or water can act
B2 (c) · 1 mark · Contrasts with addition polymers lacking these linkages or points out why polyesters degrade faster
Worked solution
a) Poly(chloroethene) is made by subjecting chloroethene monomers to high pressure, heat, and an initiator. The double bonds open up and join together to form a long chain, producing the polymer.
b) Addition polymers like poly(chloroethene) are not easily biodegradable because they are chemically inert and do not have reactive functional groups. This prevents bacteria and other microorganisms from breaking the chains down.
c) Polyesters such as PLA are more biodegradable because their polymer chains contain ester linkages. These can be hydrolysed by water and enzymes naturally found in the environment or produced by microorganisms, causing the polymers to break down more easily than addition polymers, which lack such linkages.