Cambridge International AS and A Level Chemistry 35: Polymerisation

Polymerisation is Cambridge International Chemistry 9701 Topic 35. The A Level boundary covers polyester and polyamide formation from paired or self-condensing monomers, repeat-unit and monomer deduction, classification of polymerisation and degradation by light or hydrolysis.

1. Condensation polymerisation

Condensation polymerisation joins bifunctional monomers and eliminates a small molecule at each new link. Water is lost when carboxylic acids react, while hydrogen chloride is lost when acyl chlorides react.

Monomers need two reactive ends to build long chains. A monofunctional molecule can terminate growth but cannot by itself form a linear high polymer.

The repeating link identifies the reaction family more reliably than the carbon skeleton alone.

2. Polyester from diol and dicarboxylic acid

Each hydroxyl group of a diol reacts with a carboxyl group of a dicarboxylic acid, forming ester links and eliminating water.

The repeat unit contains residues from both monomers. Remove hydroxyl from the acid group and hydrogen from the alcohol group at each joining site, but preserve all remaining atoms.

Polymer brackets cut through bonds continuing to neighbouring repeat units.

3. Polyester from diol and dioyl chloride

A diol reacts with a dioyl chloride to form a polyester and hydrogen chloride. The acyl chloride route is more reactive and proceeds through addition-elimination at each carbonyl.

The dioyl chloride supplies both carbonyl sides of ester links; the diol supplies oxygen-containing chain segments.

Account for two reactive acyl-chloride ends per dioyl-chloride molecule.

4. Polyester from a hydroxycarboxylic acid

A hydroxycarboxylic acid contains both required functions in one molecule. Its hydroxyl reacts with another molecule's carboxyl group, creating an ester link and water.

The repeat unit is derived from one monomer residue rather than alternating residues from two monomers.

Do not join hydroxyl to hydroxyl or carboxyl to carboxyl.

5. Polyamide from diamine and dicarboxylic acid

Each amino group of a diamine condenses with a carboxyl group of a dicarboxylic acid, forming amide links and water.

The repeat unit retains one diamine residue and one diacid residue. The amide nitrogen keeps one hydrogen when the starting amine group is primary.

Preserve carbon counts on both sides of every carbonyl.

6. Polyamide from diamine and dioyl chloride

A diamine reacts with a dioyl chloride to form a polyamide and hydrogen chloride. Nitrogen attacks the acyl carbon, followed by chloride elimination.