Explain why poly(alkenes) are difficult to biodegrade
Link the chemically inert hydrocarbon backbone of poly(alkenes) to their resistance to biodegradation and persistence.
Section 35 · Polymerisation
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 property helps explain why poly(alkenes) are difficult to biodegrade?
What you will learn
- Recognise poly(alkenes) as chemically inert in the syllabus context
- Explain difficulty of biodegradation
- Connect slow breakdown with persistence
A stable hydrocarbon chain persists
Poly(alkenes) have long chains of strong C–C and C–H bonds and are chemically inert in the syllabus context. They do not contain ester or amide links that are readily broken by hydrolysis.
Because they are difficult for biological processes to break down, poly(alkene) waste can persist and accumulate if it is not managed. This is a reason disposal can be difficult, not a claim that every polymer behaves the same way.
Separate biodegradation from other disposal routes
Resistance to biodegradation does not mean a poly(alkene) can never be changed by any process. Mechanical recycling, combustion or other treatments are different processes with their own limits and environmental considerations.
Use the specified polymer class and connect its chemical inertness to slow biological breakdown. Avoid claiming that a plastic disappears simply because it fragments into smaller pieces.
Pause and explain
What may happen when non-biodegradable poly(alkene) waste is not managed?
Worked example
Explain why discarded poly(ethene) can remain in the environment for a long time.
Show the worked solution
- Poly(ethene) is a poly(alkene).
- Its saturated hydrocarbon backbone is chemically inert and resists biological breakdown.
- Persistent material can accumulate if not collected and managed.
Answer Poly(ethene) is difficult to biodegrade because its chemically inert C–C/C–H backbone resists biological breakdown, so discarded material can persist and accumulate.
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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.
Give a linked explanation for the persistence of poly(propene) waste.
Give me a hint
Name its polymer family, chemical property and consequence.
Compare my reasoning
- Poly(propene) is a poly(alkene).
- Its hydrocarbon backbone is chemically inert and difficult to biodegrade.
- Unmanaged waste can persist and accumulate.
Poly(propene) is a chemically inert poly(alkene), so biological breakdown is difficult and discarded material can persist and accumulate.
Look for these in your work
- Class named
- Property linked
- Consequence stated
A student says that a plastic is biodegradable because it breaks into small visible fragments. What distinction should the answer make?
Give me a hint
Compare fragmentation with biological decomposition of the material.
Compare my reasoning
- Fragmentation changes particle size.
- Biodegradation means biological breakdown of the material.
- Small fragments may still persist.
Fragmentation alone does not prove biodegradation; small pieces can remain as persistent polymer material.
Look for these in your work
- Processes distinguished
- Definition applied
- Conclusion limited
A city proposes mechanical recycling for poly(alkene) packaging. Does chemical inertness prove recycling is impossible? Explain.
Give me a hint
Separate resistance to biological breakdown from mechanical processing.
Compare my reasoning
- Inertness explains biodegradation difficulty.
- Mechanical recycling is a different process.
- Collection, sorting and processing still affect practical success.
No. Chemical inertness helps explain resistance to biodegradation but does not prove mechanical recycling is impossible; practical recycling depends on collection and processing.
Look for these in your work
- Property scope limited
- Processes distinguished
- Practical factor identified
Common mistakes
- Calling poly(alkenes) readily biodegradable
- Equating fragmentation with complete biodegradation
- Claiming all polymers are inert
- Saying inert means impossible to recycle or treat
What can you explain now?
Which property helps explain why poly(alkenes) are difficult to biodegrade?
Compare with the explanation
Their chemically inert hydrocarbon backbone
The stable carbon-chain structure resists biological breakdown.
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Make it stick
How does the poly(alkene) backbone help explain slow biodegradation and persistence?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.