Relate linkages to intermolecular forces, hydrolysis products and practical disposal choices.
Separate forces between chains from bonds within chains
Polyester chains have London forces and permanent dipole interactions associated with polar ester groups. A typical polyester repeat has no O–H donor, so do not draw extensive polyester-to-polyester hydrogen bonding as though every ester oxygen carried H. End groups or other substituents can change that description.
Polyamides containing N–H groups can hydrogen-bond between N–H hydrogen on one chain and carbonyl O on another. These attractions help explain strength and often high melting/softening temperatures. Chain length, packing, rigidity and crystallinity also matter, so it is not valid to assert that every polyamide melts above every polyester.
Terylene is used in fibres and packaging; nylon 6,6 in durable fibres and engineering components; Kevlar in strong reinforcing/protective fibres. Kevlar’s rigid aromatic backbone and effective interchain interactions contribute to its properties. Relate a named structural feature to a use rather than merely calling the bonds “strong”.
Diagram placeholder
Interchain polyamide hydrogen bonds to add
Labels to include:
- Two distinct polyamide chains
- Cδ⁺=Oδ⁻ with O lone pairs
- N–Hδ⁺ groups
- Dashed O:···H–N hydrogen bonds
- Near-linear O···H–N arrangement
- Covalent backbone bonds distinct from dashed interchain bonds
Draw the dashed attraction to H attached to N, not a new covalent bond directly between O and N. Keep each chain’s amide bonds intact. June 2023 Paper 2 Q04.6 assessed clear donors, acceptor lone pairs and bond geometry.
Polar ester and amide links can be cleaved
Polyesters and polyamides contain hydrolysable links in their backbones. Acidic or alkaline hydrolysis breaks these into shorter chains and ultimately monomer-derived species. Polyalkene backbones contain strong largely non-polar C–C and C–H bonds and lack the equivalent hydrolysable ester/amide link.
Acid hydrolysis gives carboxylic acids; amino groups are protonated in sufficiently acidic solution. Alkaline hydrolysis gives carboxylate ions and neutral amine groups. If the question asks for structures in the reaction mixture, include those charges instead of automatically drawing neutral starting monomers.
| Polymer | Acidic products | Alkaline products |
|---|---|---|
| PET | Ethane-1,2-diol + benzene-1,4-dicarboxylic acid | Diol + benzene-1,4-dicarboxylate salt |
| Nylon 6,6 | Hexanedioic acid + doubly protonated hexane-1,6-diamine | Hexanedioate salt + hexane-1,6-diamine |
| Polypeptide with neutral side chains | Amino acids with NH₃⁺ and COOH at low pH | Amino acids with NH₂ and COO⁻ at high pH |
Hydrolysable does not mean rapid breakdown everywhere
Hydrolysable links make biological or chemical breakdown possible under suitable conditions. Actual degradation rate depends on access to water, temperature, enzymes, chain packing, surface area and structure. Many polyamides and polyesters persist for long periods in ordinary environments even though they can be hydrolysed under stronger conditions.
Do not equate bio-based, biodegradable and compostable. A polymer can come from biological feedstock yet remain resistant to degradation. A compostability claim depends on a specified environment and test; it is not permission to litter. For the exam comparison, explain why the polar link offers a cleavage site and a polyalkene backbone does not.
Compare options using a stated criterion
An evaluation should weigh energy, emissions, material quality, sorting, costs and local facilities rather than announce one method is always best. Mixing incompatible polymers can reduce recycled-product quality. Burning waste is not the same as uncontrolled burning, and neither makes carbon emissions disappear.
| Method | Potential advantage | Limitation |
|---|---|---|
| Mechanical recycling | Preserves material and can reduce demand for new feedstock | Needs collection, sorting and cleaning; contamination/heat can affect properties |
| Chemical recycling or hydrolysis | Can recover useful monomer-derived chemicals for suitable polymers | Requires energy, reagents and separation; not every route is economical |
| Energy recovery by controlled incineration | Reduces waste volume and can recover energy | Releases CO₂; combustion products need control, especially halogen-containing plastics |
| Landfill | Can contain material that cannot presently be recovered | Uses space and discards useful resources; persistent plastics remain |
| Managed biological treatment for suitable materials | Can process materials designed for the relevant conditions | Needs the correct conditions and waste stream; not universal for all plastics |
Quick checks
Original Finesse questions. Reveal the indicative worked solutions after attempting each question; these are not official AQA mark allocations.
Q1. Identify the hydrogen-bond donor and acceptor in a typical polyamide.Show answer
The donor is H covalently bonded to N. The acceptor is a lone pair on a carbonyl oxygen, usually on another chain or another chain segment.
Q2. Why are polyalkenes not hydrolysed in the same way as polyesters?Show answer
They lack polar ester/amide links that can undergo hydrolytic cleavage. Their backbone is predominantly strong C–C and C–H bonds.
Q3. What happens to the diamine fragment when nylon 6,6 is completely hydrolysed in strong acid?Show answer
It is protonated at both amino groups, giving H₃N⁺(CH₂)₆NH₃⁺, alongside hexanedioic acid. Suitable counter-ions are present in the acidic solution.
Q4. Why does the presence of ester bonds not prove a plastic will quickly disappear in seawater?Show answer
Hydrolysis rate also depends on conditions and accessibility, including temperature, water access, enzymes and chain packing. A hydrolysable bond does not guarantee rapid environmental degradation.
Q5. Give one benefit and one limitation of mechanical recycling.Show answer
It can retain useful polymer material and reduce new feedstock demand. Collection, sorting and contamination control are needed, and processing can reduce quality; explain the trade-off for the stated material.
Sources
Sources and examiner guidance (reviewed 2 October 2026)
- AQA 7405 organic chemistry specification — 3.3.12 coverage and required skills.
- Chemrevise: Polymers — Coverage checklist; explanations, data exercises and quick checks on this page are original Finesse material.
- AQA June 2023 Paper 2 mark scheme — Q04.5–04.6 pp19–21 and report Q04.5–04.6 p4: finite-chain end groups and correctly drawn polyamide hydrogen bonding.
- AQA June 2023 Paper 2 examiner report — Read alongside the question-specific marking guidance; not a universal wording checklist.
Finesse Tuition is not endorsed by AQA or Chemrevise. All explanations and examples here are our own.