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, 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:

An ester link – joining the two carbon chains R and R’ R and R’ could be the same or different chains

An amide link – joining the two carbon chains R and R

  • Polyesters : the two monomers need 1. anOH\textsf{OH} group and 2. a COOH\textsf{COOH} group.

  • 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 📌

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.

  • 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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