6.2.3 Polyesters and polyamides

Condensation polymerisation

a reaction in which monomers are linked together into a polymer with the release of a small molecule, such as water, as a by-product

Polyester

monomers are joined together by ester linkages in a long chain to form the polymer

How are polyesters made

made from a monomer containing a carboxylic acid group and an alcohol group

Repeat unit (revision)

A specific arrangement of atoms that occurs in the structure over and over again. Repeat units are included in brackets, outside of which is the symbol n.

Polyesters made from two monomers each containing two functional groups

One monomer is a diol
One monomer is a dicarboxylic acid

Polyamides

condensation polymers that contain the amide functional group

Polyamides from one monomer with two functional groups

Amide bond is formed and water is lost

Polyamides from two monomers each with two functional groups

can be made with a diamine and a dicarboxylic acid (or acyl chloride)

What are the two reagents you can use to hydrolyse condensation polymers?

Hot aqueous alkali
Hot aqueous acid

Hydrolysing polyesters

alkali hydrolysis forms a carboxylate ion salt

Hydrolysing polyamides

the H+ in acid hydrolysis can protonate COO- to COOH and NH₂ to NH₃+ in the monomers produced. there isn't a proton in base hydrolysis so this doesn't happen.

Summary of acid and alkali hydrolysis on condensation polymers (regarding NH2 and COOH)

Hot aqueous acid = NH3+ and COOH
Hot aqueous alkali= NH2 and COO-