Polymerisation Mechanisms Compared

 
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The following two tables compare some of the aspects of addition polymerisation (e.g. the free radical polymerisation of ethene) with condensation polymerisation (e.g. the formation of Nylon-6,6 or PET).

The first table compares the properties of the reaction types, while the second table shows the differences over the course of the reaction.

CondensationAddition
any two molecular species can reactmolecular species can react only with active centres
chains start short and steadily growchains are long at all times
most monomer gone early in reaction some monomer remains until end of reaction
reactions relatively slow, generate little heatreactions relatively fast, generate lots of heat

Early in the reaction Midway through the reaction Late in the reaction
Addition Lots of monomer,
a few long chains,
(a few smaller chains)
Less monomer,
more long chains,
(more smaller chains)
Little bit of monomer,
lots of long chains,
some middle-sized chains
Condensation Some monomer,
lots of short chains
Some short chains,
lots of middle-sized chains
Some middle-sized chains,
lots of long chains