9701 · 35.3
Degradable polymers flashcards
Revision flashcards for Cambridge 9701 Degradable polymers (syllabus 35.3). Flip, recall, then mark a real past-paper question.
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Why are polyalkenes, like poly(ethene), non-biodegradable?
Their backbone consists of strong, non-polar C-C and C-H sigma bonds. They lack a polar bond or site for nucleophilic attack by water or enzymes, making them chemically inert and resistant to hydrolysis.
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What is a biodegradable polymer?
A polymer that can be broken down into smaller, harmless molecules by the action of microorganisms (like bacteria and fungi) and environmental conditions. This process typically involves hydrolysis.
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Which two functional groups are commonly found in biodegradable polymers to allow for hydrolysis?
Ester (–COO–) and amide (–CONH–) linkages. These groups are polar and can be hydrolysed.
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What are the hydrolysis products of a polyester like poly(lactic acid), PLA?
PLA is made from a hydroxycarboxylic acid monomer. Its hydrolysis (with water, catalysed by acid/alkali/enzymes) yields the original monomer, lactic acid (2-hydroxypropanoic acid).
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What is a photodegradable polymer?
A polymer designed to break down into smaller fragments upon exposure to light, particularly ultraviolet (UV) radiation.
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What structural feature makes a polymer photodegradable?
The presence of carbonyl groups (C=O) within the polymer backbone. The C=O group absorbs UV light, which provides the energy to break adjacent C-C bonds, initiating degradation.
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What is the key chemical difference between biodegradation and photodegradation?
Biodegradation is a chemical process, primarily hydrolysis, facilitated by microorganisms. Photodegradation is a photochemical process initiated by UV light causing bond fission, often creating radicals.
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Give an example of a common biodegradable polyester.
Poly(lactic acid) or PLA, derived from renewable resources like corn starch or sugar cane. It's used in compostable packaging and medical implants.
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What are the conditions for the hydrolysis of a polyester?
The reaction with water is slow but can be catalysed by acids (H⁺(aq)), alkalis (OH⁻(aq)), or enzymes.
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Why is adding carbonyl groups to a polyalkene chain a strategy for making it photodegradable?
The C=O group acts as a chromophore, absorbing UV energy. This weakens and eventually breaks the adjacent C-C bonds in the non-polar chain, which would otherwise not be affected by UV light.
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What is a potential drawback of photodegradable polymers?
They break down into smaller plastic fragments (microplastics), which can still persist in the environment and cause harm. They don't necessarily mineralise into CO₂, H₂O, and biomass like fully biodegradable polymers.