35.2 Predicting the type of polymerisation
- Syllabus
- 9701–2028–2029
- Topic
- 35.2
- Level
- A2
Learning objectives
Predict polymerisation type from the monomer's chain-forming groups
Inspect every monomer for groups that can form a chain. A polymerisable C=C can open and join monomers by addition. A complementary pair of bifunctional groups can react repeatedly by condensation to form ester or amide links while eliminating a small molecule.
| Monomer evidence | Predicted route | Chain-forming event | Small molecule |
|---|---|---|---|
| one or more alkene monomers, using C=C | addition | C=C opens to make new C-C backbone bonds | none |
| diol + diacid/dioyl chloride, or hydroxycarboxylic acid | condensation | repeated ester-link formation | H2O or HCl |
| diamine + diacid/dioyl chloride, aminocarboxylic acid or amino acids | condensation | repeated amide-link formation | H2O or HCl |
If a monomer contains both C=C and condensation-capable groups, the structure may support more than one possible route. Identify which groups the proposed polymerisation uses rather than classifying from the mere presence of one familiar group.
The number of different monomers does not decide the type: two different alkenes can form an addition copolymer, while one hydroxycarboxylic or aminocarboxylic acid can self-condense.
Deduce polymerisation type from links in the polymer backbone
Trace the main polymer backbone through more than one repeat. A continuous C-C backbone produced from opened alkene bonds indicates addition polymerisation. Repeated ester -CO-O- or amide -CO-NH- links within the backbone indicate condensation polymerisation.
| Polymer-section evidence | Deduction | Reason |
|---|---|---|
| carbon-carbon backbone with substituents hanging from it | addition | alkene pi bonds opened; no small molecule was eliminated |
| ester links in backbone | condensation, polyester | alcohol and acid/acyl-chloride ends joined |
| amide/peptide links in backbone | condensation, polyamide | amine and acid/acyl-chloride ends joined |
Judge the backbone, not side chains. An addition polymer may carry -CN, halogen, aryl or other functional substituents without those groups lying in the chain-forming backbone.
Do not rely on the polymer name or on oxygen/nitrogen appearing anywhere. Locate the repeated backbone linkage and show how it could arise from C=C opening or small-molecule-eliminating condensation.