Lesson 11 of 12
Choosing a polymer
Functional groups explain creasing, water response and chemical resistance.
A-Level 8873, revised syllabus (2026-2027)
I can explain all named polymer structure-property-use comparisons.Syllabus
Syllabus 8873, 9(p). Explain all named polymer structure-property-use comparisons.
I can predict polymer physical properties from structure.Syllabus
Syllabus 8873, 9(q). Predict polymer physical properties from structure.
Choose the material for the job
Functional groups explain creasing, water response and chemical resistance.
A good comparison of materials is a chain of reasoning. Name the difference in structure. Explain how that changes the interactions or reactions. Then link this to the use. Writing only "it is strong" or "it is polar" does not explain why one polymer is the better choice.
| Polymer | Condensed repeat-unit representation | Feature to inspect |
|---|---|---|
| PET, poly(ethylene terephthalate) | [-O-CH2-CH2-O-C(=O)-C6H4-C(=O)-]n | Ester links in the backbone; the two substituted positions of the aromatic ring are opposite one another. |
| Nylon 6,6 | [-NH-(CH2)6-NH-C(=O)-(CH2)4-C(=O)-]n | Amide links provide N-H donors and carbonyl O acceptors for interchain hydrogen bonding. |
| PVA, poly(vinyl alcohol) | [-CH2-CH(OH)-]n | Many OH side groups can hydrogen-bond with water. |
| PVC, poly(vinyl chloride) | [-CH2-CHCl-]n | C-Cl bonds are polar, but the chain lacks the repeated OH groups that provide strong hydration in PVA. |
| PP, poly(propene) | [-CH2-CH(CH3)-]n | A hydrocarbon backbone and methyl side groups; no ester link to hydrolyse in aqueous alkali. |
PET fabric creases slightly less than nylon 6,6 in the syllabus comparison. Nylon has amide groups that form many hydrogen bonds between chains. When the fabric is bent, especially when damp, some of these bonds break and new ones form in the new position, which holds the crease in. PET has polar ester groups but no N-H or O-H groups along its chain to donate hydrogen bonds, so this effect is smaller. PET still has attractions between chains. Neither fabric is fully crease-proof, and how the fabric is made and treated also matters.
PVA can dissolve in water and is used in eye drops. Its many OH groups form hydrogen bonds with water, so the chains can become surrounded by water and spread out. PVC is water-resistant and is used in raincoats. Its C-Cl bonds are polar, but being polar is not enough to dissolve. It does not have PVA's many OH groups to hydrogen bond with water, so water cannot pull its chains apart. The chlorine is covalently bonded, so it is not like a chloride ion in solution.
Choose PP rather than PET for strongly alkaline cleaning solutions. Alkali can hydrolyse the ester links in PET, cutting its chains into shorter pieces and weakening the container. PP has no ester links to hydrolyse, and its hydrocarbon chain resists this attack. This choice is about chemical resistance. Stiffness alone does not decide it.
Worked exampleUse supplied structure to recommend a material
Polymer X contains many neutral -C(=O)-O- links in its backbone. Polymer Y has a -CH2-CH(CH3)- backbone. Which is the better candidate for a reusable container holding concentrated aqueous alkali, and what additional evidence would help?
Try it first. Then show the worked stepsHide the worked steps
- X contains ester links, which can undergo alkaline hydrolysis and cleave the chain.
- Y is a polyalkene-type hydrocarbon structure with no corresponding hydrolysable link, so it is the stronger chemical-resistance candidate.
- For a real selection, still compare supplied data on temperature resistance, mechanical strength and long-term compatibility. The functional-group argument identifies a major risk but does not establish every performance property.
Y is preferred on the stated chemical criterion. A defensible answer names the ester link and the consequence of backbone cleavage.
Check your understanding
PVA dissolves in water. Must its repeat unit contain ions?
Show the answer
No. Its many OH groups form hydrogen bonds with water.
Solubility needs attractions to water that make up for the attractions broken. Hydrogen bonds from OH groups can do this without ions.