6.6.1Organic Chemistry and Analysis
Condensation Polymers — OCR A Level Chemistry A H432 Revision Notes & Topical Questions
5 min read 4 parts Lesson 20 of 33
Section 1 of 4Condensation Polymerisation
Condensation polymers form when monomers with two functional groups join and eliminate a small molecule each time.
Polyesters
- A dicarboxylic acid (or diacyl chloride) reacts with a diol, forming ester links –COO– and releasing water (or HCl).
Polyamides
- A dicarboxylic acid (or diacyl chloride) reacts with a diamine, forming amide links –CONH– and releasing water (or HCl).
Bifunctional monomers
- Each monomer needs a functional group at both ends so that the chain can keep growing in two directions.
Same-molecule monomers
- An amino acid,
- or a hydroxycarboxylic acid, can join with itself because it has both groups,
- such as lactic acid forming polylactic acid.
Acid chlorides
- Using a diacyl chloride in place of a diacid makes the reaction faster and irreversible, with HCl released instead of water.
Section 2 of 4Important Examples
Important Examples
Nylon-6,6
- This polyamide forms from hexane-1,6-diamine and hexanedioic acid (or hexanedioyl dichloride), with a six-carbon chain on each side of every link.
PET
- Poly(ethylene terephthalate) is a polyester made from benzene-1,4-dicarboxylic acid and ethane-1,2-diol.
Polypeptides
- Proteins are natural polyamides made from different amino acids joined by peptide links.
Intermolecular forces
- Polyamides have hydrogen bonding between chains,
- and polyesters have permanent dipole–dipole attractions between their C=O groups.
| Feature | Addition polymer | Condensation polymer |
|---|---|---|
| Monomers | Alkenes with C=C | Two functional groups per monomer |
| By-product | None | H₂O or HCl |
| Link in chain | C–C | Ester or amide |
| Hydrolysed? | No | Yes, in acid or alkali |
Section 3 of 4Breakdown and Environmental Aspects
1
Ester and amide links are polar, so water molecules can attack them when catalysed by acid or alkali.
2
This hydrolysis gives back the original monomers or their salts, unlike the unreactive C–C backbone of polyalkenes.
3
Condensation polymers are therefore more readily broken down, and some such as polylactic acid are biodegradable.
4
Polymers that hydrolyse can sometimes be chemically recycled by reversing the polymerisation.
5
Addition polymers persist for much longer, so waste plastics from them can build up in the environment.
6
Polyesters such as PET are spun into fibres or moulded into bottles, and polyamides such as nylon are used in ropes, clothing and gears.
Section 4 of 4Exam Checklist & Tips
6.6.1 – Key Points for the Exam
- Condensation polymerisation Joining of monomers with loss of a small molecule such as H₂O or HCl.
- Polyester A polymer with ester links in the chain.
- Polyamide A polymer with amide links in the chain.
- Monomer A small molecule that joins to others to make a polymer.
Common Mistakes
- Saying condensation polymerisation produces only the polymer, with no small molecule.
- Using a monomer with only one functional group, which would stop the chain growing.
- Claiming polyesters cannot be hydrolysed because they are polymers.
- Mixing up the linksesters have –COO–, amides have –CONH–.
Last updated:
\n