Explain hydrolysis of polyester and polyamide links
Acidic or alkaline hydrolysis can break ester and amide links in polyesters and polyamides under suitable conditions.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 35. Track the functional groups, repeat-unit connectivity and small-molecule by-products. Written practice is self-checked
Before you begin
- Recognise alkenes, carboxylic acids, acyl chlorides, alcohols, amines, amides and ester linkages.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which link is hydrolysed in a polyester?
What you will learn
- Identify hydrolysable ester and amide links
- Explain chain cleavage by acidic or alkaline hydrolysis
- Relate hydrolysis to biodegradation without overclaiming conditions
Hydrolysis breaks condensation links
Polyesters contain ester links, –COO–, and polyamides contain amide links, –CONH–. In hydrolysis, water participates in breaking these links; acidic or alkaline conditions can promote chain cleavage.
Breaking links divides a long polymer into smaller molecules or residues. The polymer class and link type explain why these condensation polymers can be biodegradable by hydrolysis in suitable environments.
Keep the syllabus claim bounded
The syllabus states that polyesters and polyamides are biodegradable by acidic and alkaline hydrolysis. It does not mean every item breaks down instantly in ordinary water or that all polymers share this behaviour.
Rate and extent depend on polymer structure and conditions. Use the idea to distinguish these hydrolysable links from the chemically inert carbon backbone of poly(alkenes).
Pause and explain
Which two conditions are named for hydrolysis-related biodegradation of polyesters and polyamides?
Worked example
Compare which links are broken when a polyester and a polyamide undergo hydrolysis.
Show the worked solution
- Identify the characteristic link in each polymer.
- Hydrolysis cleaves the link between residues.
- Connect chain cleavage to biodegradation under suitable conditions.
Answer Hydrolysis can cleave –COO– ester links in a polyester and –CONH– amide links in a polyamide, breaking their chains into smaller residues.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain how alkaline hydrolysis can shorten a polyester chain.
Give me a hint
Focus on the ester links between residues.
Compare my reasoning
- The polymer contains –COO– links.
- Hydrolysis cleaves ester bonds between chain residues.
- The long chain becomes shorter fragments.
Alkaline hydrolysis can cleave the polyester's ester links, separating residues and shortening the chain.
Look for these in your work
- Link named
- Hydrolysis applied
- Chain effect stated
Compare hydrolysis sites in a polyester and a polyamide.
Give me a hint
Name the characteristic link in each polymer.
Compare my reasoning
- A polyester has –COO– links.
- A polyamide has –CONH– links.
- Hydrolysis can cleave these condensation links.
Hydrolysis cleaves ester links in a polyester and amide links in a polyamide, breaking each polymer chain into smaller residues.
Look for these in your work
- Polyester link correct
- Polyamide link correct
- Common process explained
A student says every polymer biodegrades by hydrolysis because it is exposed to rain. Correct the overgeneralisation.
Give me a hint
Compare condensation links with poly(alkene) backbones and consider conditions.
Compare my reasoning
- Polyesters and polyamides have hydrolysable ester/amide links.
- Poly(alkenes) have chemically inert carbon backbones.
- Hydrolysis and biodegradation depend on polymer structure and suitable conditions.
The claim is too broad: polyesters and polyamides can biodegrade through hydrolysis of their ester or amide links under suitable conditions, whereas poly(alkenes) are chemically inert and difficult to biodegrade.
Look for these in your work
- Classes distinguished
- Link chemistry used
- Scope corrected
Common mistakes
- Saying hydrolysis breaks the C–C backbone of poly(alkenes)
- Claiming instant breakdown in any water
- Confusing photodegradation with hydrolysis
- Treating every polymer as biodegradable
What can you explain now?
Which link is hydrolysed in a polyester?
Compare with the explanation
Ester link, –COO–
Hydrolysis can break the ester connection between residues.
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Make it stick
Which links hydrolyse in polyesters and polyamides, and how does that differ from poly(alkenes)?
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