BRAINCAKELow and High Density Polythene
Poly(ethene) can be made in two quite different forms by changing the reaction conditions. The monomer is the same, but the chain shape is different, and that changes the properties.
Low-density poly(ethene), LDPE, is made at very high pressure (about 200 MPa) and about 200 °C, with a trace of oxygen as an initiator. It forms by a free-radical mechanism, and the chains are highly branched. The branches stop the chains packing closely, so the van der Waals forces between them are weaker. LDPE has a lower density (about 0.92 g cm–3), a lower melting point (about 110 °C) and is soft and flexible. Uses: carrier bags, food film, squeezy bottles.
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Key terms in this lesson
- polymer
- A long-chain molecule built from many repeating monomer units joined together.
More in Alkenes
- Reaction with COncnetrated Sulfuric Acid
- Asymmetrical Alkenes
- Reaction with Water
- Addition Polymers
- Identifying the Repeating Group
- Identifying the Monomer
- Biodegradability
- Solutions to Plastic Pollution
All 23 lessons in Alkenes · All AQA AS-level Chemistry topics