Example 1
Give the repeating unit from CH2=CHCl.
Addition opens the C=C and gives [–CH2–CHCl–]n. The chlorine substituent remains on the same carbon; no water is released.
Year 12 · SACE Stage 2
Polymer links, cross-linking and biodegradability
Match monomers, repeating units and polymer structures to properties.
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Method and worked examples
Addition polymerisation joins suitable unsaturated monomers without eliminating a small molecule. An alkene C=C opens to form a carbon-chain repeating unit. Condensation polymerisation joins multifunctional monomers while releasing small molecules, commonly water; polyester and polyamide links are recognisable in their backbones. A repeating unit is the section that reproduces the chain, including the bonds continuing into neighbouring units.
Thermoplastics can soften on heating because chains can move past one another. Extensive permanent cross-links prevent thermosets from simply melting and flowing. Cross-link density and intermolecular interactions affect rigidity, elasticity and strength. Bio-based describes feedstock origin, while biodegradable describes breakdown under specified biological conditions. A renewable feedstock does not automatically make a polymer biodegradable; accessible cleavable links and the disposal environment both matter.
Example 1
Example 2
A polymer backbone includes repeated –CO–O– links. Identify its class and likely hydrolysis site.
It is a polyester. Hydrolysis can break the ester C(=O)–O link, regenerating alcohol-derived and acid-derived groups under the stated conditions.
Watch out: Feedstock origin and biodegradability are separate properties; polymer structure and breakdown conditions determine biodegradation.