Polymerisation in alkenes

• polymers are extremely large molecules formed from many thousands of repeat units of smaller molecules known as monomers
• unsaturated alkene molecules undergo addition polymerisation to produce long saturated chains containing no double bonds
• many different polymers can be formed, each with its own specific properties depending on the monomer used
• industrial polymerisation is carried out a high temp and high pressure using catalysts
• • addition polymers have high molecular masses
  • synthetic polymers are usually named after the monomer that reacts to form their giant molecules, prefixed by 'poly'
• • a repeat unit is the specific arrangement of atoms in the polymer molecule that repeats over and over again
  • the repeat unit is always written in square brackets
  • after the bracket you place a letter n to show that there is a large number of repeats
• make sure polymerisation equations are balanced - will need the letter n before the monomer and outside the bracket after the repeat unit in the polymer
• Poly(ethene):

  • addition polymers are usually made up of one type of monomer unit
  • e.g. poly(ethene) is made by heating large number of ethene monomers at high pressure
  • one of the most commonly used polymers - supermarket bas, shampoo bottles and toys
• • poly(ethene) made by accident by Eric Fawcett and Reginald Gibson
  • carrying out high-pressure experiments with ethene at a chemical plant in Cheshire
  • test vessel leaked, allowing trace of O2 to contaminate fresh sample of ethene
  • following day found a white, waxy residue had been produced
• • poly(ethene) manufactured in large quantities using carefully controlled processes
  • depending on method used, different densities of poly(ethene) can be made that have different structures properties and uses
  • high density poly(ethene) (HDPE) has linear chains - gives plastic some strength - ideal for toys, detergent bottles and water pipes
  • Low density poly(ethene) (LDPE) has branched chains - little strength but flexible - ideal for use in plastic films and plastic bags
• poly(chloroethene):

  • poly(vinyl chloride) or PVC can be prepared to make a polymer that is flexible or rigid
  • pipes, films and sheeting, ducts and profiles, insulation and cable sheathing, bottles, flooring, fabric treatments, moulded articles
• propene = poly(propene)

  • toys, packing crates, guttering, uPVC windows and fibre for types of ropes
• phenylethene/ styrene = poly(phenylethene) or poly(styrene):

  • packaging material, food trays and cups due to thermal insulating properties
• tetrafluoroethene = poly(tetrafluoroethene) (PTFE, Teflon):

  • coating for non-stick pans, permeable membrane for clothing and shoes and cable insulation