A2 · Practice questions · Polymer deductions

Cut at the links.

Six original Cambridge-style questions on polymer deductions.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Find the link, cut it, add back water.

C–C backbone only: addition; restore the C=C.
–COO– or –CONH– in the chain: condensation.
Cut: OH back on C=O, H back on O or N.
Polyamides hydrogen bond chain to chain.

Analysis

[3 marks]

A section of a polymer is –NH(CH₂)₄NHCO(CH₂)₃CO–NH(CH₂)₄NHCO(CH₂)₃CO–. (a) Identify the type of polymer. (b) Give the structures of the two monomers.

(a) A polyamide (condensation polymer). ✓
(b) Butane-1,4-diamine, H₂N(CH₂)₄NH₂. ✓
Pentanedioic acid, HOOC(CH₂)₃COOH (or its diacyl dichloride ClOC(CH₂)₃COCl). ✓

Recall

[2 marks]

Draw the repeat unit of the polymer formed from 3-hydroxypropanoic acid, HOCH₂CH₂COOH, and name the type of polymer.

–OCH₂CH₂CO–. ✓
A polyester, formed by condensation with loss of water. ✓

Analysis

[3 marks]

For each monomer, state whether it forms an addition or a condensation polymer: (a) CH₂=CHC₆H₅, (b) H₂NCH(CH₃)COOH, (c) CH₂=CHCOOH.

(a) Addition: it has a C=C. ✓
(b) Condensation: it has NH₂ and COOH groups (gives a polyamide). ✓
(c) Addition through the C=C under normal conditions; the single COOH cannot by itself give a condensation chain. ✓

Explain

[3 marks]

Explain why nylon-6,6 has a higher melting point than poly(ethene) of similar chain length.

Nylon chains contain N–H and C=O groups. ✓
The H on N of one chain forms hydrogen bonds with a lone pair on the O of a C=O on a neighbouring chain. ✓
Poly(ethene) has only id-id forces; hydrogen bonds need more energy to overcome, so nylon melts higher. ✓

Analysis

[2 marks]

A polymer section is –CH₂CCl₂CH₂CCl₂–. Give the monomer and explain how you know the type of polymerisation.

Monomer: 1,1-dichloroethene, CH₂=CCl₂. ✓
The backbone is carbon only, with no ester or amide links, so it is an addition polymer. ✓

Explain

[2 marks]

Suggest why poly(lactic acid) chains cannot hydrogen bond to each other, whereas protein chains can.

Poly(lactic acid) is a polyester: its chain has C=O and C–O but no H attached to O or N. ✓
Protein chains have N–H groups that act as hydrogen bond donors to C=O groups on other chains. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.