Given a section of polymer, can you say how it was made and what it was made from? Spot the links, cut them in the right place, and put back the atoms that left. Then use the structure to predict how the chains hold together.
To deduce monomers from a condensation polymer, find each ester (–COO–) or amide (–CONH–) link, break the C–O or C–N bond, and add back OH to the carbonyl carbon and H to the O or N (or Cl to the carbonyl carbon if a diacyl dichloride is asked for). An addition polymer has a backbone of carbon atoms only; its monomer is found by taking a two-carbon repeat unit and putting back the C=C. A monomer with a C=C bond undergoes addition; monomers with two reactive groups (OH, NH2, COOH, COCl) undergo condensation. Properties follow from the intermolecular forces between chains: the N–H and C=O groups of polyamides form hydrogen bonds between chains, which makes nylon and Kevlar strong and high-melting.
Work through each example: find the repeating pattern first, then cut at the links.
| Polymer section | Link | Monomers |
|---|---|---|
| –OCH2CH2OOC(CH2)4CO–OCH2CH2OOC(CH2)4CO– | ester | HOCH2CH2OH and HOOC(CH2)4COOH |
| –NHCH(CH3)CO–NHCH2CO– | amide (peptide) | alanine H2NCH(CH3)COOH and glycine H2NCH2COOH |
| –OCH(CH3)CO–OCH(CH3)CO– | ester | one monomer: CH3CH(OH)COOH |
| –CH2CH(CN)–CH2CH(CN)– | none: C–C only | addition: CH2=CHCN |
Four quick checks. Each correct answer earns XP and records this skill on your profile.
A polymer chain contains only carbon atoms in its backbone. What type of polymer is it?
Which monomer would undergo addition polymerisation?
When an amide link in a polymer is hydrolysed back to monomers, which groups are re-formed?
What force between chains makes nylon-6,6 much stronger than poly(ethene)?
Toggle between the addition and condensation examples in the simulator. Compare the all-carbon backbone of a poly(alkene) with the ester and amide links of a condensation polymer.
| Feature | Addition polymer | Condensation polymer |
|---|---|---|
| monomer | contains C=C | two reactive groups (OH, NH2, COOH, COCl) |
| by-product | none | H2O or HCl at every link |
| backbone | carbon atoms only | contains O or N in ester or amide links |
| repeat unit vs monomer | same atoms as the monomer | monomers minus the small molecules |
When cutting an amide link, the C=O stays with the acid monomer and the N–H with the amine: do not split the C=O away from its carbon. A polymer with a C–C backbone and side groups such as –CN or –COOCH3 is still an addition polymer, even if the side group is an ester. Polyesters cannot hydrogen bond chain to chain, because they have no H on O or N.
Unlocks once the four checks above are done. Worth more XP, written to A Level Paper 4 standard.
A section of a polymer is –OCH2CH2CH2OOCC6H4CO–. Which pair of monomers could form it?
A protein fragment is –NHCH2CO–NHCH(CH3)CO–NHCH2CO–. How many different amino acids does it contain?
Which polymer contains an ester group but is an addition polymer?
Why does Kevlar have a much higher tensile strength than poly(propene)?
This skill is now recorded on your profile. Keep the chain going.