Polymers

4.2 Organic compounds

5.1 Air and oxygen

Polymers

  1. Polymerisation

    1. Alkenes can be used to make polymers such as poly(ethene) and poly(propene)
    2. In polymerisation reactions, many small molecules, called monomers, join together to form very large molecules called polymers
    3. Individual carbon-carbon double bonds are broken and replaced with single bonds
    4. Diagram: Polymerisation diagram

  2. Properties

    1. The properties of polymers depend on what they are made from and conditions they are made under: low-density (LD) and high-density (HD) poly(ethene) are produced using different catalysts and reaction conditions
    2. LD poly(ethene), under very high pressures and a trace of oxygen, forms randomly branched chains that cannot pack closely together, hence its lower density
    3. HD poly(ethene), using a catalyst at 50 °C and a slightly raised pressure, forms straighter chains which can pack more closely, hence its higher density; it has a higher softening temperature and is stronger than LD poly(ethene)
    4. Thermosoftening polymers consist of individual, tangled polymer chains with weak intermolecular forces between the chains that are easily overcome when heated, making the polymer become soft
    5. Thermosetting polymers consist of polymer chains with cross-links of strong covalent bonds between them, making the polymer rigid and heat-resistant

  3. Uses

    1. Polymers have many useful applications, with new uses being developed, such as new packaging materials, waterproof coatings for fabrics, dental polymers, wound dressing, hydrogels and smart materials (including shape memory polymers)
    2. Biodegradable polymers made from cornstarch, to preserve crude oil supplies, have been developed so that they break down more easily, with uses such as plastic bags