Addition polymerisation joins many small alkene molecules, called monomers, into one very long chain molecule, a polymer. In each monomer the C=C double bond opens (the π bond breaks) and the carbon atoms form new single bonds to neighbouring monomers.n CH2=CH2 → -[CH2-CH2]-n Here n, the number of monomers joined, is very large (often thousands). The polymer is named by putting the monomer name in brackets after 'poly': ethene gives poly(ethene).
Other important addition polymers:• propene → poly(propene)
• chloroethene, CH2=CHCl → poly(chloroethene), PVC
• tetrafluoroethene, CF2=CF2 → poly(tetrafluoroethene), PTFEIndustrially these reactions need high pressure with an initiator, or a catalyst.Key features:
• the polymer is the only product, so the atom economy is 100%
• the polymer has the same empirical formula as its monomer
• the chain is saturated, with strong, non-polar C-C and C-H bonds, so addition polymers are very unreactiveWorked example: a sample of poly(ethene) has Mr = 28 000. Ethene has Mr = 28. The number of monomer units is n = 28 000 ÷ 28 = 1000.
Other important addition polymers:• propene → poly(propene)• chloroethene, CH2=CHCl → poly(chloroethene), PVC
• tetrafluoroethene, CF2=CF2 → poly(tetrafluoroethene), PTFEIndustrially these reactions need high pressure with an initiator, or a catalyst.Key features:
• the polymer is the only product, so the atom economy is 100%
• the polymer has the same empirical formula as its monomer
• the chain is saturated, with strong, non-polar C-C and C-H bonds, so addition polymers are very unreactiveWorked example: a sample of poly(ethene) has Mr = 28 000. Ethene has Mr = 28. The number of monomer units is n = 28 000 ÷ 28 = 1000.