Predicting the type of polymerisation — common mistakes

A common exam question gives you the structure of a polymer and asks you to identify the monomer(s). For an addition polymer, locate the repeating carbon backbone and mentally 're-form' the double bond between the two central carbons of the unit. For a condensation polymer, identify the ester or amide linkage and 'break' it by hydrolysis (adding $H_2O$), adding -OH to the carbonyl carbon and -H to the oxygen or nitrogen atom to regenerate the original functional groups.

Yes, provided the monomer molecule contains two different functional groups that can react with each other. A classic example is an amino acid (containing $-NH_2$ and $-COOH$ groups) or a hydroxycarboxylic acid (containing $-OH$ and $-COOH$ groups).

Both contain amide linkages. The key difference is their origin and monomer composition. Polypeptides are natural polymers made in biological systems from the 20 common $\alpha$-amino acids. Synthetic polyamides, like Nylon, are man-made from monomers such as diamines and dicarboxylic acids, which are not typically amino acids.

This describes how the polymer chains grow. In 'chain-growth' (addition), an active site (e.g., a radical) adds monomers one by one very rapidly, so long chains form quickly while much monomer is still unreacted. In 'step-growth' (condensation), any two molecules can react (monomer + monomer, dimer + monomer, dimer + dimer, etc.), so the average molecular mass of all molecules in the pot increases slowly and in steps.