Chemistry • Year 12 • Module 8 • Lesson 16
Polymers: Structure, Properties & Applications
Lock in the core vocabulary: addition vs condensation polymers, common polymer examples, thermoplastics, thermosets, structure–property relationships and microplastics.
1. Term–definition match
Match each definition to the correct term. Terms: addition polymer, condensation polymer, monomer, thermoplastic, thermosetting polymer, cross-linking, microplastic, branching, polyamide, polyester. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 1.1 | A polymer formed when alkene monomers join across a double bond; no small-molecule by-product is released. | |
| 1.2 | A polymer formed by stepwise reaction of bifunctional monomers, with the loss of a small molecule such as water or HCl. | |
| 1.3 | The small repeating unit from which a polymer chain is built. | |
| 1.4 | A polymer that softens on heating and re-hardens on cooling; its chains are held by intermolecular forces rather than covalent cross-links. | |
| 1.5 | A polymer with extensive covalent bonds between adjacent chains; it decomposes rather than melts when strongly heated and cannot be remoulded. | |
| 1.6 | Covalent bonds between adjacent polymer chains; increases rigidity, tensile strength and heat resistance. | |
| 1.7 | Plastic particles smaller than 5 mm formed by the breakdown of larger plastic items; persistent in ecosystems and food chains. | |
| 1.8 | Side chains extending off the main polymer backbone; reduces crystallinity and density, often increasing flexibility. | |
| 1.9 | A condensation polymer with amide (–CO–NH–) links in the backbone; example: nylon-6,6. | |
| 1.10 | A condensation polymer with ester (–COO–) links in the backbone; example: PET. |
2. True or false — with correction
Circle T or F. If false, write the corrected version on the line below. 10 marks (1 T/F, 1 correction where needed)
2.1 Both addition and condensation polymers release a small molecule (such as water) during polymerisation. T / F
2.2 PTFE (polytetrafluoroethylene) is an addition polymer with a fluorinated carbon chain that gives it very high chemical resistance. T / F
2.3 A thermosetting polymer can be remelted and reshaped repeatedly because its chains are joined only by weak intermolecular forces. T / F
2.4 Branching in a polymer reduces the ability of chains to pack together closely, which generally decreases density and increases flexibility. T / F
2.5 Plastic fragments in the ocean eventually fully biodegrade into harmless molecules on a human timescale. T / F
3. Cloze — complete the passage
Fill in each blank using one word or phrase from the word bank. Each term is used once only. 9 marks
Addition polymers form from _______________ monomers with no by-product. _______________ polymers, by contrast, form when functional groups react and a small molecule is removed. Nylon-6,6 contains _______________ links in its backbone, while PET contains _______________ links. The rigidity of a _______________ such as Bakelite comes from extensive covalent bonds between chains. A _______________ polymer can be remelted because its chains are held by weaker intermolecular forces. A high degree of _______________ in a polymer generally increases tensile strength and melting point. Large plastic items that fragment into tiny particles produce _______________, which persist in ecosystems. One strategy to recover useful feedstocks from waste polymer rather than simply melting it is called _______________.
4. Function recall
Answer each in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
4.1 What is the key structural difference between an addition polymer and a condensation polymer in terms of by-products?
4.2 Why does cross-linking prevent a polymer from being remelted and reshaped?
4.3 Why is the microplastic problem considered an environmental issue even if the original plastic item is removed from view?
4.4 How does adding polar functional groups to a polymer chain affect the strength of intermolecular forces and the melting point?
5. Classify and justify
For each polymer, state whether it is an addition or condensation polymer and whether it is a thermoplastic or a thermosetting polymer. Give one structural justification for each classification. 8 marks
| Polymer | Addition or condensation? | Thermoplastic or thermosetting? | Structural justification |
|---|---|---|---|
| Polyethylene (PE) | |||
| Nylon-6,6 | |||
| Bakelite (epoxy type) | |||
| PET (polyethylene terephthalate) |
Q1 — Term–definition matches
1.1 addition polymer • 1.2 condensation polymer • 1.3 monomer • 1.4 thermoplastic • 1.5 thermosetting polymer • 1.6 cross-linking • 1.7 microplastic • 1.8 branching • 1.9 polyamide • 1.10 polyester.
Q2 — True/False with correction
2.1 False. Correction: only condensation polymers release a small molecule (e.g. water, HCl) during polymerisation. Addition polymers form from alkene monomers with no small-molecule by-product.
2.2 True. PTFE is an addition polymer formed from tetrafluoroethylene monomers; the fully fluorinated chain gives it exceptional chemical resistance.
2.3 False. Correction: thermosetting polymers cannot be remelted because they contain extensive covalent cross-links between chains; they decompose on heating. It is thermoplastics that soften on heating because their chains are held by weaker intermolecular forces.
2.4 True. Branching prevents chains from packing closely, reducing crystallinity and density; this is why branched LDPE is more flexible than linear HDPE.
2.5 False. Correction: most synthetic plastics do not biodegrade on human timescales. They break into progressively smaller pieces called microplastics that persist in ecosystems without truly disappearing.
Q3 — Cloze answers (in order)
alkene • condensation • amide • ester • cross-linking • thermoplastic • crystallinity • microplastics • chemical recycling
Q4.1 — Addition vs condensation: by-products
Addition polymers form from alkene monomers that join across the double bond, releasing no by-product. Condensation polymers form when bifunctional monomers react repeatedly, releasing a small molecule such as water or HCl at each step.
Q4.2 — Why cross-linking prevents remelting
Cross-linking creates covalent bonds between adjacent polymer chains, forming a permanent three-dimensional network. Heating provides thermal energy but cannot break these covalent bonds without causing chemical decomposition, so the material does not soften or flow; it decomposes instead.
Q4.3 — Microplastic environmental problem
Even when large plastic items are removed from view, they may have already fragmented into microplastics (<5 mm). These tiny particles are persistent, spread through food webs and water systems, and can enter the bodies of organisms. They do not truly disappear: fragmentation is not biodegradation.
Q4.4 — Polar groups and melting point
Polar functional groups such as –OH, –NH– or –C=O can form stronger dipole–dipole interactions or hydrogen bonds between adjacent chains. Stronger intermolecular forces require more energy to overcome, raising the polymer’s melting point and generally increasing rigidity.
Q5 — Classify and justify
| Polymer | Addition or condensation | Thermoplastic or thermosetting | Justification |
|---|---|---|---|
| Polyethylene (PE) | Addition | Thermoplastic | Forms from ethene monomers (alkene) with no by-product; chains are not covalently cross-linked so the material can be remelted. |
| Nylon-6,6 | Condensation | Thermoplastic | Forms from diamine and diacid monomers with loss of water; amide links in backbone. Chains are not permanently cross-linked, so nylon can be remelted. |
| Bakelite | Condensation | Thermosetting | Forms by condensation (phenol + formaldehyde with loss of water); extensive covalent cross-links between chains prevent remelting. |
| PET | Condensation | Thermoplastic | Forms from diol and diacid monomers with loss of water; ester links in backbone. Chains are not permanently cross-linked so PET can be remelted and recycled. |