Write the free radical mechanism for the polymerization of ethene.

Chain initiation

The chain is initiated by free radicals, Ra•, produced by the reaction between some of the ethene and the oxygen initiator.

Chain propagation

Each time a free radical hits an ethene molecule a new longer free radical is formed.

Ra• + CH₂ = CH₂→ RaCH₂CH₂•

RaCH₂CH₂• + CH₂ = CH₂→ RaCH₂CH₂CH₂CH₂ •

Chain termination

Eventually two free radicals hit each other producing a final molecule. The process stops here because no new free radicals are formed.

Ra(CH₂)_m• + •(CH₂)_n Ra → Ra(CH₂)_m(CH₂)_nRa

Because chain termination is a random process, polyethene will be made up of chains of all sorts of different lengths.