Condensation Polymers

In condensation polymerisation, monomers with two functional groups join and release a small molecule (H₂O or HCl). Polyesters: diol + dicarboxylic acid (or diacyl chloride), e.g. PET from benzene-1,4-dicarboxylic acid and ethane-1,2-diol, linked by –COO–. Polyamides: diamine + dicarboxylic acid, e.g. nylon-6,6 (hexane-1,6-diamine + hexanedioic acid) and Kevlar, linked by –CONH–; hydrogen bonds between chains give strength. Proteins are natural polyamides. Unlike poly(alkenes), condensation polymers can be hydrolysed at their polar links (acid or alkali), making some biodegradable (e.g. PLA).

Cambridge 9701 Paper 4Edexcel YCH11 WCH15AQA 7405 Paper 2≈ 45 minRevision 1 · updated 2026-11-01

Section 1 of 14

Learning objectives

Describe formation of polyesters and polyamides.
Draw repeat units and deduce monomers.
Explain properties using intermolecular forces.
Explain why condensation polymers can be hydrolysed.

Pause and think

Why can nylon be broken down by hot acid, but poly(ethene) can't?

Section 2 of 14

Core idea

Start hereFrom stockings to body armour

Nylon stockings and Kevlar vests are both polyamides: the same link, different monomers.

The big idea

Monomers with two functional groups join and lose a small molecule each time. The polar ester or amide links can be hydrolysed, unlike poly(alkenes).

1. Building a repeat unit

Nylon-6,6

$\mathrm{HOOC(CH_2)_4COOH+H_2N(CH_2)_6NH_2}$
Hexanedioic acid and hexane-1,6-diamine.
$\mathrm{-CO(CH_2)_4CO-NH(CH_2)_6NH-}$
OH from the acid and H from the amine leave as water.
$2n\,\mathrm{H_2O}$
Two amide links per repeat unit.

Worked exampleRepeat unit Mr

$M_r$ of nylon-6,6 repeat unit, C₁₂H₂₂N₂O₂?

Goal: $M_r$ .
Strategy: Add atomic masses.

$12(12)+22(1)=166$
C and H.
$166+2(14)+2(16)=226$
N and O.

Answer226.

✓ Check146 + 116 − 36 = 226 ✓.

Summary

Polyesters –COO–, polyamides –CONH–.
Water or HCl lost.
Hydrolysable; some biodegradable.

Condensation polymer: Polymer formed with loss of a small molecule.
Polyamide: Polymer with amide links.

HistoryNylon, 1935. Wallace Carothers at DuPont made nylon-6,6 in 1935. Nylon stockings went on sale in 1939, and sold four million pairs in a few hours in New York.

Fun factBulletproof vests. Kevlar is five times stronger than steel by weight, thanks to its flat, aligned chains held together by hydrogen bonds.

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