Read repeat structures, recover monomers and apply pH-specific hydrolysis rules.
Method and worked examples
Locate each –CO–O– ester or –CO–NH– amide link in a polymer backbone. Split the link between carbonyl carbon and O or N. Add OH to the carbonyl fragment and H to the other fragment to recover the parent acid and alcohol or amine. Keep every carbon, including carbonyl carbons, in its original fragment.
Acidic hydrolysis gives carboxylic acids; amine products are protonated in strong acid. Alkaline hydrolysis gives carboxylate ions and neutral alcohols or amines. To build a repeat, reverse that operation: remove linking H and OH and show bonds continuing across both repeat boundaries. A monomer bearing both suitable end groups can self-condense into a polyester or polyamide.
Example 1
Recover monomers from polyester repeat –OCH2CH2OCOCH2CH2CO– under acidic hydrolysis.
The OCH2CH2O fragment becomes HOCH2CH2OH. The COCH2CH2CO fragment becomes HOOCCH2CH2COOH. The monomers are ethane−1,2−diol and butanedioic acid.
Example 2
Recover neutral monomer structures from polyamide repeat –NH(CH2)6NHCO(CH2)4CO– before applying any acid–base conditions.
Restore H on each amide N and OH on each acid-derived carbonyl. The parent structures are H2N(CH2)6NH2 and HOOC(CH2)4COOH. Under alkaline hydrolysis the latter appears as−OOC(CH2)4COO−.
Watch out:Use the hydrolysable functional-group link; ordinary ester/amide hydrolysis preserves the carbon skeletons of the monomer fragments.
Polyester and polyamide structure conversions | Year 12 Chemistry | Ascent Arcade