Addition Polymerisation

Understanding Addition Polymerisation

  • Addition polymerisation is a type of chemical reaction where monomers with double bonds combine together to form a long chain polymer with single bonds.
  • This process involves many small molecules, known as monomers, joining together to form a large molecule, which is the polymer. The double bond in the monomer molecule breaks, allowing the monomers to link together.
  • Often, it’s the process by which plastics are made.

Examples of Addition Polymerisation

  • A common example is the formation of poly(ethene), commonly known as polyethylene. The monomer is ethene (C2H4), and it forms a polymer of repeating units: [-CH2-CH2-]n.

  • Poly(propene), commonly known as polypropylene, also forms in a similar way from propene (C3H6) monomers.

General Mechanism

  • The general mechanism in addition polymerisation involves the breakage of the carbon-carbon double bond in the monomer. One of the bonds breaks, leaving each carbon atom with an unpaired electron.
  • These free electrons form the new single bonds with neighbouring monomers, resulting in a long chain polymer.

Uses of Addition Polymers

  • Poly(ethene) or polythene is used in making plastic bags, films and bottles.
  • Poly(propene) or polypropylene is used in making ropes, carpets, car bumpers and microwave-proof containers.
  • Poly(chloroethene), often referred to as PVC or polyvinyl chloride, is hard and resistant to chemical attack, making it suitable for use in guttering, window frames and pipework.

Environmental Concerns

  • Many addition polymers are non-biodegradable, meaning that they do not break down in the environment over time. This means they can contribute to environmental pollution.
  • Recycling of addition polymers can help to mitigate this, although not all plastics can be efficiently recycled.
  • Additionally, the burning of plastics can release toxic gases, causing air pollution, and their manufacture uses non-renewable resources like crude oil.