Recognise that some polymers can be degraded by light
Identify photodegradation as a route for some polymers and avoid generalising it to all polymers.
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
What is the term for degradation caused by light?
What you will learn
- Recognise light as a cause of degradation for some polymers
- Use photodegradation terminology
- Distinguish light degradation from biodegradation and hydrolysis
Light can break down some polymer chains
Some polymers can be degraded by the action of light; this is photodegradation. Light-driven chemical changes can break or alter polymer chains, reducing their size or strength.
The syllabus outcome is deliberately limited to some polymers. Do not state that all polymers photodegrade at the same rate or that exposure to light guarantees complete mineralisation.
Name the process precisely
Photodegradation is different from biodegradation, which involves biological processes, and hydrolysis, which breaks bonds by reaction with water under acidic or alkaline conditions.
A material becoming brittle or fragmenting under light is evidence of degradation, but the final environmental fate of fragments depends on further processes and conditions.
Pause and explain
Which statement matches the syllabus scope for light degradation?
Worked example
A polymer becomes brittle and fragments after prolonged light exposure. What syllabus idea does this illustrate?
Show the worked solution
- The change is caused by light exposure.
- Some polymers can undergo photodegradation.
- Do not infer that all fragments have fully biodegraded.
Answer It illustrates photodegradation: light can degrade some polymers, although fragmentation alone does not show complete biodegradation.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
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.
Name and define the process when a polymer chain is altered by light.
Give me a hint
Use the cause in the process name.
Compare my reasoning
- The cause is light.
- Use the prefix photo-.
- Describe degradation without claiming full biological breakdown.
Photodegradation is degradation of a polymer caused by light; it does not by itself establish complete biodegradation.
Look for these in your work
- Correct term
- Cause stated
- Limit respected
A product label says ‘light degradable’. What can you safely infer from the syllabus outcome, and what remains unproven?
Give me a hint
Keep the claim to the stated process.
Compare my reasoning
- Some polymer materials can be degraded by light.
- The statement does not prove the material fully biodegrades.
- Do not infer degradation rate or final products without evidence.
Light may degrade the polymer, but the claim alone does not prove complete biodegradation, a particular rate, or harmless final products.
Look for these in your work
- Outcome applied
- Biodegradation distinguished
- Evidence limit stated
A student labels sunlight-driven chain scission as hydrolysis. Correct the classification.
Give me a hint
Ask whether water is the reacting cause or light is the stated cause.
Compare my reasoning
- The stated cause is light exposure.
- That is photodegradation.
- Hydrolysis specifically involves bonds reacting with water.
It is photodegradation if light causes the chain change; hydrolysis is a separate process involving reaction with water.
Look for these in your work
- Cause identified
- Term corrected
- Hydrolysis contrasted
Common mistakes
- Claiming every polymer is photodegradable
- Calling light-driven chain breakdown hydrolysis
- Equating fragmentation with biodegradation
- Claiming light alone guarantees complete mineralisation
What can you explain now?
What is the term for degradation caused by light?
Compare with the explanation
Photodegradation
The name identifies light as the cause.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
What does photodegradation mean, and why should it not be equated automatically with biodegradation?
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.