SACE Chemistry — Stage 2
Polymers — Flashcards & Quiz
Polymers are large molecules built from repeating monomer units, and SACE Chemistry Stage 2 distinguishes addition polymerisation (alkene monomers join via opening the C=C double bond) from condensation polymerisation (monomers join with loss of a small molecule, usually water). You need to explain how polymer structure determines physical properties and biodegradability, and draw representative repeat units.
Key Points
- Addition polymerisation: alkene monomers (e.g. ethene, propene, styrene) join by breaking the C=C double bond. No small molecule lost. Examples: polyethylene, PVC, polystyrene.
- Condensation polymerisation: two functional groups react, releasing a small molecule (usually water). Examples: nylon, polyester, proteins, carbohydrates.
- Thermoplastics soften on heating (linear chains, weak intermolecular forces between chains). Thermosets decompose rather than melt (cross-linked, covalent bonds between chains).
- Repeat unit: the smallest section of the polymer that, when repeated, builds the whole molecule. Drawn in square brackets with a subscript n.
- Biodegradability depends on the presence of linkages enzymes can break — ester, amide, and glycosidic bonds are biodegradable; C–C chains (polyethylene) are not.
- Properties depend on chain length, branching, crystallinity, and intermolecular forces. Longer, straighter chains give higher density, stronger, more crystalline material.
Common Mistakes to Avoid
- Confusing addition (no byproduct) with condensation (water byproduct) polymerisation.
- Writing the monomer as the repeat unit without opening the double bond for addition polymers.
- Claiming all polymers are biodegradable — polyethylene and PVC persist for centuries.
- Mixing up thermoplastics and thermosets — the difference is cross-linking.
- Forgetting that natural polymers (proteins, starch, cellulose, DNA) are all condensation polymers.
Exam Strategy
SACE Stage 2 polymer questions ask you to draw repeat units, classify polymerisation types, or explain property differences. Method: (1) identify the monomer(s), (2) decide addition or condensation, (3) draw the repeat unit (opening double bonds for addition; removing water for condensation), (4) link structure to properties. Name real-world examples for full marks.
Sample Flashcards
Q1: How are disaccharides and polysaccharides formed from glucose, and what are their formulae and functions?
Monosaccharide units join by condensation reactions, releasing one water molecule per link. Two glucose units form a disaccharide such as maltose: 2C₆H₁₂O₆ → C₁₂H₂₂O₁₁ + H₂O. Many glucose units form a polysaccharide (C₆H₁₀O₅)ₙ. Functions: energy storage (starch in plants, glycogen in animals) and structural support (cellulose in plant cell walls). Ribose and deoxyribose are sugars in nucleic acids.
Q2: How does condensation polymerisation differ from addition polymerisation?
Condensation polymerisation joins monomers by removing a small molecule (usually H₂O) at each linkage. Monomers must have TWO functional groups (difunctional). The polymer has a different empirical formula from the monomer. Examples: polyesters (from diacid + diol) and polyamides/nylon (from diacid + diamine).
Sample Quiz Questions
Q1: Starch, glycogen and cellulose are all polymers of glucose.
Answer: TRUE
All three are polysaccharides made by condensation of glucose units, with the formula (C₆H₁₀O₅)ₙ.
Q2: Nylon is a condensation polymer formed from a dicarboxylic acid and a diamine.
Answer: TRUE
Nylon (polyamide) is formed by condensation of a dicarboxylic acid and a diamine. Each amide bond (-CONH-) formation releases one water molecule.
Revision Tip
Monomer-to-repeat-unit drawings are drillable — build a Revizi deck with 8+ monomers asking you to draw the polymer repeat unit from scratch.
Related Concepts
Last updated: 9 October 2026 · 2 sample flashcards · 2 sample quiz questions