A9.1 Addition and Condensation Polymers
Addition Polymerisation involves the joining together of many monomer molecules to produce one polymer chain and no other products. Addition polymers always have a continuous chain of carbon atoms.
Polyalkenes like polyethene and polychloroethene are the obvious examples – see section A5.
Condensation Polymerisation involves joining together monomer molecules where there are two different functional groups which react together, join the monomer molecules and eject a small molecule in the process. This small molecule could be
H2O,Β HCl\textsf H_\textsf2\textsf {O, HCl}
or
NH3\textsf{NH}_3
.
The reactive functional groups are on opposite ends of the monomer molecules – so the two molecule chains are joined together leaving a tell-tale link which could be:
Figure 9.1 An ester link
An ester link – joining the two carbon chains R and R’ R and R’ could be the same or different chains
Figure 9.2 An amide link
An amide link – joining the two carbon chains R and R
​
  • Polyesters : the two monomers need 1. an
    OH\textsf{OH}
    group and 2. a
    COOH\textsf{COOH}
    group.
Figure 9.3 Polyester
  • Here we have a diol (ethan-1,2-diol) and benzene-1,2-dicarboxylic acid The molecule ejected during polymerisation is
    H2O\textsf{H}_\textsf2\textsf O
    .
  • The OH group of the dicarboxylic acid could be replaced by a chlorine atom, in which case we would get the same polymer, but an
    HCl\textsf{HCl}
    molecule would be ejected.

Author's tip
πŸ“Œ

Note the ester link. You can spot the C=OCO in esters (when written out in full)!
  • Polyamides: the two monomers need 1. an
    OH\textsf{OH}
    group and 2. a
    NH2\textsf{NH}_\textsf2
    group Here we have a dicarboxylic acid and a diamine. The molecule ejected dicarboxylic acid during the polymerisation is
    H2O\textsf{H}_\textsf2\textsf{O}
    . Note the amide link.
  • The OH group of the dicarboxylic acid could be replaced by a chlorine atom, in which case we would get the same polymer, but an
    HCl\textsf{HCl}
    molecule would be ejected.
Figure 9.4 Polyamide
  • Carbohydrates and Proteins, often present in natural fibres, are examples of naturally occurring condensation polymers.
  • Nylon and Polyesters are examples of synthetic (man-made) polymers.
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1. an ester link
2. An amide link