Small repeats. Big differences.
HDPE has relatively little branching, so chains pack closely. LDPE has more branching and packs less efficiently, giving lower density and greater flexibility. In polypropene, the arrangement of side groups (tacticity) affects how regularly chains pack.
Polyethene, polypropene and PTFE have carbon-chain backbones. Polyesters, polyamides and PLA contain characteristic ester or amide linkages. Some of these bonds can be hydrolysed under suitable conditions.
Biodegradability depends on chemistry and conditions, not simply whether a material is made from plants. Temperature, water, microorganisms and accessible bonds matter. Industrially compostable does not mean rapid breakdown in the ocean.
Join the building blocks
Three ethene units illustrate the polyethene backbone. Dots represent continuation; terminal chemistry is omitted.
Explore: Compare repeating units and relate chain features to material properties.
Name the linkage found in a polyester and explain one possible route for chain breakdown.
- Identify an ester bond in the chain.
- Hydrolysis cleaves the linkage, shortening the chain.
Answer: Ester linkages; hydrolysis can break these bonds under suitable conditions.
Assumed knowledge
Packing describes how neighbouring chains fit together.
Learning checkpoints & source
YOUR SYLLABUS CHECKPOINT- Relate chain branching and packing to density and strength.
- Distinguish addition and condensation linkages.
- Explain structural contributions to biodegradability.