Polymerisation
The addition polymerisation of chloroethene produces poly(chloroethene),
commonly called PVC (polyvinyl chloride). It is generally carried out
in water as a batch process lasting from 4 to 6 hours, and requires
the use of an initiator to start the reaction. The temperature is normally
fairly low (50 - 75°C), but with pressures up to 13 atmospheres.
An addition polymerisation reaction can be regarded as having three
stages:
Initiation
An initiator reacts with monomer to make a product
that is suitable for further reaction
Propagation
Additional monomer molecules add to the reactive
product repeatedly, extending the polymer chain
Termination
The reactive end of the chain undergoes a reaction
that will not lead to further propagation
Initiators
The initiators are organic peroxides, which easily split to form free
radicals, with a single un-bonded electron. It is this that initially
reacts with the chloroethene monomer.
Polymerisation Process
If you cannot see the above animation click
here for a static diagram of the process
Improvements
New formulations for polymerisation, specialised heating techniques, and
automation of processes has resulted in a doubling of the output of reactors,
at the same time as reducing the use of energy by over 30%.
