Chemistry • Year 12 • Module 7 • Lesson 23
Polymers: Properties, Applications & Environmental Impact
Recall core vocabulary, match polymer types to their structural features, and build the conceptual map linking polymer structure to bulk properties and environmental fate.
1. Fill in the blanks
Complete the paragraph below using terms from the word bank. Each term is used once only. 10 marks
Three structural variables control polymer properties. Increasing _____________ (1) raises tensile strength and melting point because longer chains entangle more. Introducing _____________ (2) prevents close chain packing, reducing density and making the polymer more flexible — this is why _____________ (3) (recycling code 4) is soft and used in plastic bags. Higher _____________ (4) in a polymer allows chains to pack into ordered regions, increasing hardness. When covalent bonds form between adjacent chains through _____________ (5), the polymer forms a permanent 3D network called a _____________ (6), which cannot be re-melted. In contrast, a _____________ (7) such as _____________ (8) (recycling code 1) softens on heating and can be reshaped, making it generally recyclable. Most synthetic polymers are non-_____________ (9), so physical breakdown by UV light and mechanical stress produces _____________ (10) (fragments smaller than 5 mm) that accumulate in ecosystems.
2. Term–definition matching grid
Write the matching term from the box below in the right-hand column. 10 marks
| # | Definition | Matching term |
|---|---|---|
| 2.1 | A polymer formed when monomers join together with no by-product released; all atoms in the monomer appear in the chain. | |
| 2.2 | A polymer formed with loss of a small molecule (e.g. water) at each step; contains functional groups in the backbone. | |
| 2.3 | Covalent bonds between adjacent polymer chains that produce a rigid, permanent 3D network. | |
| 2.4 | A polymer with extensive cross-links that decomposes rather than melts on heating; cannot be re-moulded or conventionally recycled. | |
| 2.5 | Plastic fragments smaller than 5 mm produced by UV degradation and mechanical stress; widespread pollutants in marine and terrestrial environments. | |
| 2.6 | A biopolymer derived from renewable plant starch (e.g. corn) that can be composted under industrial conditions; used in compostable packaging. | |
| 2.7 | Linear (unbranched) polyethylene with tightly packed chains; hard, opaque, and rigid — used in milk bottles and pipes. Recycling code 2. | |
| 2.8 | A number 1–7 stamped on plastic products to indicate the polymer type and inform sorting for recycling. | |
| 2.9 | The resistance of a material to being pulled apart along its length; increased by longer chains and greater chain entanglement. | |
| 2.10 | The ability of a polymer to be broken down by microorganisms; most synthetic polymers lack this property, while biopolymers such as PLA and PHA can degrade under appropriate conditions. |
3. True or false — with correction
Circle T or F. If false, write the corrected version on the line. 10 marks (1 T/F + 1 correction where needed)
3.1 Thermoset polymers melt at a very high temperature but can be re-moulded if enough heat is applied. T / F
3.2 LDPE and HDPE are different polymers because they are made from different monomers. T / F
3.3 Increasing the degree of branching in a polyethylene chain generally raises its density and melting point. T / F
3.4 PLA (polylactic acid) is a biopolymer that can degrade in any environment including landfill and home compost. T / F
3.5 Recycling code 1 (PET) and code 2 (HDPE) have the most established recycling infrastructure in most Australian councils. T / F
4. Function recall
Answer each question in 1–2 sentences using precise chemical vocabulary from the lesson. 10 marks, 2 each
4.1 What structural feature of PTFE (Teflon) makes it chemically inert and gives it a very low surface energy?
4.2 PVC is described as having “polar C–Cl bonds” that create strong intermolecular forces. Explain how this structural feature makes rigid PVC suitable for pipes and window frames.
4.3 Why are most synthetic polymers non-biodegradable? Name the specific bond type that resists microbial degradation.
4.4 What are microplastics, and why are they particularly problematic compared to large pieces of plastic waste?
4.5 Why does nylon-6,6 have higher tensile strength than a simple polyethylene chain of the same length?
5. Build a concept map
Draw labelled arrows between the six terms below to show how they are connected. Each arrow must carry a linking phrase (e.g. "determines", "produces", "is measured by"). Aim for at least 6 labelled arrows. 6 marks
Supplied terms: chain length • cross-linking • tensile strength • thermoset • recycling • microplastics
Q1 — Fill in the blanks
(1) chain length • (2) branching • (3) LDPE • (4) crystallinity • (5) cross-linking • (6) thermoset • (7) thermoplastic • (8) PET • (9) biodegradable • (10) microplastics
Q2 — Term–definition matches
2.1 addition polymer • 2.2 condensation polymer • 2.3 cross-linking • 2.4 thermoset • 2.5 microplastics • 2.6 polylactic acid (PLA) • 2.7 HDPE • 2.8 recycling code • 2.9 tensile strength • 2.10 biodegradability
Q3 — True / false
3.1 False. Thermoset polymers do not melt at any temperature; they decompose (char) when heated because the extensive covalent cross-links cannot break free as a melt. No amount of heat causes flow.
3.2 False. LDPE and HDPE are both polyethylene; they share the same monomer (ethylene/ethene). The difference is chain architecture: LDPE has branched chains; HDPE has linear chains.
3.3 False. Increasing branching lowers density and melting point because branches prevent chains packing closely together.
3.4 False. PLA requires industrial composting conditions (above ~60 °C, controlled humidity) to degrade. It does not break down reliably in landfill, home compost, or the ocean.
3.5 True. Codes 1 and 2 have established kerbside collection and processing streams in most Australian local councils.
Q4 — Function recall
4.1 PTFE contains only C–F bonds, which are among the strongest bonds in organic chemistry and are highly non-polar. This makes the surface energetically unreactive (low surface energy) and resistant to almost all chemicals and solvents.
4.2 The C–Cl bond in PVC is polar (chlorine is more electronegative than carbon), creating permanent dipoles along each chain. Dipole–dipole forces between adjacent chains add to the London dispersion forces, producing stronger overall intermolecular forces than in non-polar polyethylene. These stronger forces hold the chains together more tightly, resisting deformation and giving rigid PVC its structural strength — making it suitable for high-pressure applications such as pipes and window frames.
4.3 Most synthetic polymers have C–C (or C–F) backbones that are non-polar and chemically inert. Microorganisms lack the enzymes needed to cleave these bonds efficiently, so the chains persist in the environment.
4.4 Microplastics are plastic fragments smaller than 5 mm. They are more problematic than larger pieces because they are easily ingested by marine organisms at multiple trophic levels, are very difficult to remove from water bodies, and can concentrate persistent organic pollutants.
4.5 Nylon-6,6 contains amide (C–N) bonds in its backbone with N–H groups that form hydrogen bonds between adjacent chains. These inter-chain hydrogen bonds add to the van der Waals forces, significantly increasing the force needed to pull chains apart (tensile strength) compared to non-polar polyethylene, which relies only on weak dispersion forces.
Q5 — Sample concept map
Award 1 mark per correct, labelled arrow (up to 6). Acceptable arrows include:
- chain length → increases → tensile strength
- cross-linking → creates → thermoset
- thermoset → cannot undergo → recycling
- recycling (absence) → contributes to formation of → microplastics
- chain length → influences → recycling (longer chains easier to re-melt when thermoplastic)
- cross-linking → increases → tensile strength