Polymerisation of Chloroethene

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.

diagram: initiator structure

Polymerisation Process

If you cannot see the above animation click here for a static diagram of the process

diagram: PVC manufacturing flow-diagram

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%.

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