AQA A-Level Chemistry: Polymers (7405) – Revision Notes

These notes condense section 3.3.12 Polymers of the AQA AS and A-level Chemistry specification (7404/7405), version 1.2, July 2026, for AS and A-level exams June 2016 onwards: 3.3.12.1 Condensation polymers and 3.3.12.2 Biodegradability and disposal of polymers. The whole section is A-level only. It is examined on A-level Paper 2, and A-level Paper 3 can test any content.

For full explanations and worked examples, read the polymers study guide. Then test yourself with the polymers practice questions. The course hub is AQA A-Level Chemistry, the printable checklist lists every specification point, and the free 10-minute diagnostics show where your gaps are. Addition polymers, PVC and plasticisers are in the alkenes revision notes.

Key definitions

Term	Meaning
Condensation polymerisation	Monomers with two functional groups join, losing a small molecule (usually H₂O) at each link
Polyester	Condensation polymer with ester links, –COO–, from a dicarboxylic acid and a diol
Polyamide	Condensation polymer with amide links, –CONH–, from a dicarboxylic acid and a diamine, or from amino acids
Repeating unit	The smallest section that repeats; for two monomers it holds one residue of each
Hydrolysis	Breaking a bond by reaction with water; for these polymers, the reverse of condensation
Biodegradable	Can be broken down in the environment, eg by hydrolysis
Chemically inert	Does not react; true of polyalkenes

The polymers you must know (3.3.12.1)

Polymer	Type	Monomers	Repeating unit	Typical uses
Terylene	polyester	benzene-1,4-dicarboxylic acid + ethane-1,2-diol	–[CO–C₆H₄–CO–O–CH₂CH₂–O]–	clothing fibres, drinks bottles
Nylon 6,6	polyamide	hexanedioic acid + hexane-1,6-diamine	–[CO–(CH₂)₄–CO–NH–(CH₂)₆–NH]–	clothing, carpets, ropes
Kevlar	polyamide	benzene-1,4-dicarboxylic acid + benzene-1,4-diamine	–[CO–C₆H₄–CO–NH–C₆H₄–NH]–	body armour, bulletproof vests, ropes

C₆H₄ is a benzene ring joined at positions 1 and 4. In the lab, nylon 6,6 is often made from hexanedioyl dichloride instead of the acid; then HCl is lost, not water.

Amino acids need only one monomer, because each has –NH₂ and –COOH. 2-aminopropanoic acid, H₂N–CH(CH₃)–COOH, gives –[NH–CH(CH₃)–CO]–.

Method: repeating unit from monomers

1. Draw the two monomers side by side, functional groups facing.
2. Remove OH from –COOH and H from –OH or –NH₂; join C to O or C to N.
3. Repeat at the other ends, so one residue of each monomer sits inside the brackets.
4. Draw extension bonds through the brackets and write n outside.
5. In an equation, show 2n H₂O (or 2n HCl from a diacyl dichloride) on the right.

Method: monomers from a section of chain

1. Find each –CO–O– or –CO–NH– link.
2. Cut between C and O, or C and N.
3. Add OH to the carbonyl carbon (gives –COOH) and H to O or N (gives –OH or –NH₂).
4. Check the monomers by counting carbons in each residue.

Small reminder. Section –O–CH₂CH₂–O–CO–(CH₂)₃–CO–O–CH₂CH₂–O–: cut the ester links and you get ethane-1,2-diol and HOOC–(CH₂)₃–COOH, pentanedioic acid.

Mr of a repeating unit

Mr(repeating unit) = Mr(monomer 1) + Mr(monomer 2) − 2 × Mr(H₂O). For nylon 6,6: 146.0 + 116.0 − 36.0 = 226.0. Number of units in a chain = Mr(chain) / Mr(repeating unit).

Intermolecular forces (3.3.12.1)

Polymer type	Forces between chains	Why
Polyalkene, eg poly(ethene)	van der Waals only	non-polar C–C and C–H bonds
Polyester, eg Terylene	van der Waals + permanent dipole–dipole	polar C=O; no H on O or N
Polyamide, eg nylon 6,6	van der Waals + hydrogen bonds	N–H on one chain, lone pair on C=O oxygen of the next
Kevlar	as polyamide, very many hydrogen bonds	flat, rigid chains line up in parallel

Stronger forces between chains → higher melting point and stronger fibres.

Hydrolysis and biodegradability (3.3.12.2)

• Polyesters and polyamides have polar C=O bonds in their links. The δ+ carbon is attacked by nucleophiles (H₂O, OH⁻), so the links can be hydrolysed. These polymers are biodegradable.
• Polyalkenes have only strong, non-polar C–C and C–H bonds. There is no δ+ carbon to attack, so they are chemically inert and non-biodegradable.

Hydrolysis	Polyester gives	Polyamide gives
Acid (H⁺, heat)	dicarboxylic acid + diol	dicarboxylic acid + ammonium salt of the diamine
Alkaline (OH⁻, heat)	carboxylate salt + diol	carboxylate salt + diamine

Disposal of polymers (3.3.12.2)

Method	For	Against
Landfill	cheap, simple, no sorting	uses land; polyalkenes persist; resource wasted
Incineration	less volume; energy for electricity	CO₂ released; PVC gives toxic HCl, which must be removed
Mechanical recycling	saves crude oil and energy; less landfill	collecting, sorting and cleaning cost money and energy; quality falls
Feedstock recycling	recovers monomers or chemicals	energy-intensive; specialist plant

Method: evaluating a disposal method

1. Name the method and the polymer(s) involved.
2. Give one advantage, linked to resources, energy or land.
3. Give one disadvantage, linked to the chemistry (non-biodegradable, CO₂, HCl from PVC, sorting).
4. If the waste is mixed, say what that means for sorting or for the gases produced.
5. End with a judgement only if the question asks you to evaluate or compare.

Links to other topics

• 3.3.4.3 Addition polymers: repeating units from C=C monomers, PVC and plasticisers.
• 3.3.9 Carboxylic acids and derivatives: ester hydrolysis in acid or alkali, and acyl chlorides reacting with amines; the same reactions make and break these polymers.
• 3.3.13 Amino acids, proteins and DNA: polypeptides are polyamides made from amino acids.
• 3.1.3 Bonding: hydrogen bonds, permanent dipole–dipole forces and van der Waals forces.

Must-know distinctions

• Addition vs condensation: addition polymers form from C=C monomers with no other product; condensation polymers form from bifunctional monomers and lose H₂O (or HCl).
• Polyester vs polyamide: –COO– vs –CONH–; dipole–dipole vs hydrogen bonds between chains.
• Acid vs alkaline hydrolysis: in acid, amines end up as ammonium salts; in alkali, acids end up as carboxylate salts.
• Inert vs biodegradable: polyalkenes inert (no polar bonds); polyesters and polyamides hydrolysable.

Quick self-test

1. Name the small molecule lost when a diol reacts with a dicarboxylic acid.
2. Give the two monomers of nylon 6,6.
3. Name the linkage in Kevlar.
4. Give one typical use of Terylene.
5. Draw the repeating unit of the polyamide from 2-aminopropanoic acid.
6. A poly(2-aminopropanoic acid) chain has Mr 7.10 × 10³. How many repeating units does it contain? (Ar: H = 1.0, C = 12.0, N = 14.0, O = 16.0)
7. Name the strongest type of force between nylon 6,6 chains.
8. Why are there no hydrogen bonds between Terylene chains?
9. Name the organic products when nylon 6,6 is heated with dilute hydrochloric acid.
10. Explain why poly(propene) cannot be hydrolysed.
11. Give one disadvantage of incinerating PVC.
12. Give the monomers from the section –NH–(CH₂)₃–NH–CO–CH₂–CO–.

Answers

1. Water.
2. Hexanedioic acid and hexane-1,6-diamine.
3. Amide (–CONH–).
4. Clothing fibres, or plastic drinks bottles.
5. –[NH–CH(CH₃)–CO]ₙ–, with extension bonds.
6. Repeating unit C₃H₅NO, Mr = 71.0; 7.10 × 10³ / 71.0 = 100.
7. Hydrogen bonds.
8. The ester link has no H bonded to O or N, so there is no δ+ H to bond to a lone pair.
9. Hexanedioic acid and the ammonium salt of hexane-1,6-diamine (hexane-1,6-diammonium chloride).
10. It has only non-polar C–C and C–H bonds, so there is no δ+ carbon for water or OH⁻ to attack.
11. Burning PVC releases toxic HCl gas (as well as CO₂).
12. H₂N–(CH₂)₃–NH₂ (propane-1,3-diamine) and HOOC–CH₂–COOH (propanedioic acid).

Where marks are usually lost

• A two-monomer repeating unit drawn with only one residue, or with two residues of the same monomer.
• Repeating units that keep –OH or –H on the ends instead of extension bonds.
• Equations that miss the 2n H₂O, or show n H₂O for a two-monomer polymer.
• Kevlar or Terylene drawn with the ring joined at the wrong positions.
• Saying polyesters form hydrogen bonds between chains.
• Saying hydrogen bonds form between N–H and N–H, rather than N–H and the C=O oxygen.
• Explaining polyalkene inertness with “weak bonds” instead of non-polar bonds and no δ+ carbon.
• Giving the free amine as a product of acid hydrolysis.
• Disposal answers with an advantage but no disadvantage, or with no chemistry.

Official syllabus

AQA, AS and A-level Chemistry specification (7404/7405), version 1.2, July 2026, for AS and A-level exams June 2016 onwards: section 3.3.12 Polymers (3.3.12.1 Condensation polymers and 3.3.12.2 Biodegradability and disposal of polymers), A-level only.