Topic 8 of 9
Condensation polymers and depolymerisation
Recognise the linkage that is made or broken.
O-Level 6092 (2026) / SEC G3 K324 (2027)
Pure onlyCondensation polymers and depolymerisation
Recognise the linkage that is made or broken.
Condensation polymerisation joins monomers with suitable functional groups, eliminating small molecules such as water. Nylon is a polyamide, with -C(=O)-NH- links. Terylene is a polyester, with -C(=O)-O- links. Different polymers may differ in their monomer units, their linkages, or both.
| Polymer | A simplified repeating pattern | Linkage |
|---|---|---|
| Nylon | [-NH-A-NH-C(=O)-B-C(=O)-]n | Amide: -C(=O)-NH- between neighbouring units |
| Terylene | [-O-A-O-C(=O)-B-C(=O)-]n | Ester: -C(=O)-O- between neighbouring units |
A and B stand for the intervening carbon-containing sections, not chemical element symbols. Follow the chain through the bracket boundary to find each linkage. These partial structures explain the polymer class without requiring industrial manufacture details or mechanisms.
Nylon: recognise the amide links
A partial chain with two carbonyl groups flanking carbon-containing segment B and NH groups flanking segment A. Open bonds at both edges continue the polymer.
Terylene: recognise the ester links
A partial chain with two carbonyl groups flanking carbon-containing segment B and O groups flanking segment A. Open bonds at both edges continue the polymer.
Worked example
Deduce a condensation repeat unit
How would HO-A-OH and HOOC-B-COOH join, and how does replacing the alcohol with H2N-A-NH2 change the polymer?
- The diol has two alcohol ends and the diacid two carboxylic-acid ends, so repeated joining can build a long chain.
- Each ester link eliminates water and connects -O-A-O- with -C(=O)-B-C(=O)-.
- With a diamine instead, -NH-A-NH- replaces the oxygen-containing segment; amide links form.
The diol/diacid gives a polyester; the diamine/diacid gives a polyamide. To deduce monomers from the chain, cut the linkages and restore -OH at acid ends and H at alcohol/amine ends.
Nylon and Terylene are useful man-made fibres: applications include clothing, curtains, fishing line, parachutes and sleeping bags. Suitability depends on properties such as strength, durability and flexibility; knowing the material name is less useful than connecting a property to the job.
- Add water under acidic conditions
Acid acts as a catalyst; heating can speed the process.
- Break ester links
Water contributes H and OH across the broken linkage.
- Recover monomers
Alcohol and carboxylic-acid groups are restored; extensive cleavage can return the original monomers.
For a chain made from HO-A-OH and HOOC-B-COOH, hydrolysis restores these two monomer types. This is depolymerisation: breaking a polymer into its monomers. It is different from merely melting the plastic, which leaves the long molecules largely intact.
Worked example
Recover both ends when a polyester is hydrolysed
A polyester repeat contains -O-A-O-C(=O)-B-C(=O)-, with the chain continuing at both ends. Deduce the two monomer types after complete acid-catalysed hydrolysis.
- Mark every -C(=O)-O- ester link, including the one at the repeat boundary.
- Break the bond between the carbonyl carbon and the single-bonded oxygen. Restore OH to each carbonyl carbon to form the two carboxylic-acid ends.
- Restore H to each alcohol-derived oxygen. Segment A has two alcohol ends; segment B has two acid ends.
HO-A-OH and HOOC-B-COOH. Water provides the H/OH; the acid is a catalyst. Cutting a C-C bond or returning only one end group would give the wrong monomers.