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: What is addition polymerisation?
Addition polymerisation occurs when many unsaturated monomer molecules (containing C=C bonds) join together by opening their double bonds. No atoms are lost — all monomer atoms appear in the polymer. The polymer has the same empirical formula as the monomer.
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: Addition polymerisation produces a small molecule such as water as a by-product.
Answer: FALSE
Addition polymerisation does NOT produce any by-products — all monomer atoms are incorporated into the polymer chain. It is condensation polymerisation that releases a small molecule.
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.
Last updated: March 2026 · 2 flashcards · 2 quiz questions