35.1 Condensation polymerisation

A diol and a dicarboxylic acid (or dioyl chloride) can link repeatedly through ester bonds, releasing water or HCl. A hydroxycarboxylic acid can self-condense in the same way.

Each monomer must have two reactive groups to extend the chain. The repeating unit contains the ester linkage –CO–O– and the polymer’s end groups depend on stoichiometric balance.

Ethane-1,2-diol plus benzene-1,4-dicarboxylic acid gives a chain containing –OCH₂CH₂OCOC₆H₄CO– repeats.

A single alcohol plus a single acid makes a small ester, not a polyester; chain growth requires at least two functional groups on each linking unit.

A diamine and a dicarboxylic acid (or dioyl chloride) can condense to form a polyamide. Aminocarboxylic acids and amino acids can also self-condense when each molecule supplies both groups.

Each amide link forms between –NH₂ and –COOH/–COCl, releasing water or HCl. Two functional groups on each linking unit allow chains to continue.

Hexane-1,6-diamine plus hexanedioic acid gives a nylon-like chain containing –NH(CH₂)₆NHCO(CH₂)₄CO– repeats.

A mixture of a monoamine and monoacid makes a small amide, not a high polymer; chain growth requires bifunctionality.

A condensation-polymer repeat unit is the smallest section that repeats after the monomers lose a small molecule such as water or HCl. Draw the new covalent link, then show the unreacted atoms at each end.

For a diol/diacid polymer, the repeat contains –O–CO–; for a diamine/diacid polymer, it contains –NH–CO–. Include the correct carbon count from each monomer.

Ethane-1,2-diol + benzene-1,4-dicarboxylic acid gives –OCH₂CH₂OCOC₆H₄CO– as the repeating section.

Do not remove atoms from the carbon skeleton or draw a terminal molecule instead of a repeating unit.

To identify condensation monomers, cut each ester or amide link at the bond formed during condensation and restore the corresponding –OH/–COOH or –NH₂ groups.

An ester link points to a diol plus dicarboxylic acid (or a hydroxycarboxylic acid); an amide link points to a diamine plus dicarboxylic acid or amino acid family.

From –O–CH₂CH₂–O–CO–C₆H₄–CO–, restore ethane-1,2-diol and benzene-1,4-dicarboxylic acid.

Do not interpret every oxygen as an alcohol group; inspect whether it sits in –CO–O– or another linkage.