ACTIVATION OF THE HIGH-PRESSURE POLYMERIZATION OF ETHYLENE INITIATED WITH ORGANIC PEROXIDES BY MEANS OF ORGANOALUMINUM COMPOUNDS

In the course of this study, an activator system consisting of an alum inium trialkyl compound and a Lewis base was tested for its suitabilit y for the radical polymerisation of ethylene at high pressure. The aim of reducing the initiator consumption and the polymerisation temperat ure was achieved with aluminium trialkyl alone without the use of a Le wis base. Among the aluminium trialkyl compounds examined, triethyl al uminium proved to be the most effective. This effectiveness is due to the increased rate of decomposition of the peroxide as a result of whi ch a larger amount of free radicals becomes available thus increasing the rate of polymerisation. By using an addition of 50 mole ppm trieth yl aluminium to 50 mole ppm tert-butyl-perpivalate in the ethylene fee d it was possible to almost double the monomer conversion at a given p olymerisation temperature and to reduce by half the consumption of per oxide initiator per kg polyethylene produced. Compared with the non-ac tivated polymerisation, the polymerisation temperature was reduced fro m 150 degrees C to 125 degrees C, the initiator consumption remaining the same. The costs of the triethyl aluminium activator are more than offset by the increased yield and the decrease in initiator consumptio n.