Organic mechanisms Low density poly(ethene), LDPE The manufacture of low density poly(ethene) is carried out at very high pressure (1000 – 3000atm) at a temperature of about 500K Ex: R – O-O – R -> 2ROfree radical formation RO + H 2 C = CH 2 -> R – O – CH 2 – CH 2 propagation R – O – CH 2 – CH 2 + H 2 C = CH 2 -> R – O – CH 2 – CH 2 – CH 2 – CH 2 Termination takes places when two radical combines

Low density poly(ethene), LDPE An average polymer molecule with about from 4 x 103 to 4 x 104 carbon atoms with many short branches which affect both degree of crystalize and density of material

High density poly(ethene), HDPE HDPE is produced by polymerizing ethene at a low temperature ( 350K) and pressure ( 1 – 50atm) using a Ziegler – Naha catalyst. The catalyst is a suspension of titanium (iv) chloride together with an alkyl aluminium compound (Al(C 2 H 5 ) 3 ). The result of polymer consist mainly of linear chains with very little branching. This gives it a higher density 0.96gcm -3 and a more rigid structure as the chains can fit together more closely. It is used to make containers and pipes