Activation of the high pressure polymerisation of ethylene initiated with organic peroxides by means of organoaluminium compounds

Abstract

In the course of this study, an activator system consisting of an aluminium trialkyl compound and a Lewis base was tested for its suitability for the radical polymerisation of ethylene at high pressure. The aim of reducing the initiator consumption and the polymerisation temperature was achieved with aluminium trialkyl alone without the use of a Lewis base.Among the aluminium trialkyl compounds examined, triethyl aluminium proved to be the most effective. This effectiveness is due to the increased rate of decomposition of the peroxide as a result of which a larger amount of free radicals becomes available thus increasing the rate of polymerisation. By using an addition of 50 mole ppm triethyl aluminium to 50 mole ppm tert-butyl-perpivalate in the ethylene feed it was possible to almost double the monomer conversion at a given polymerisation temperature and to reduce by half the consumption of peroxide initiator per kg polyethylene produced. Compared with the non-activated polymerisation, the polymerisation temperature was reduced from 150 OC to 125 O 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 consumption. ZUSAMMENFASSUNG:In dieser Arbeit wurde die Eignung eines aus einer Tkialkylaluminiumverbindung und einer Lewisbase bestehenden Aktivatorsystems fur die radikalische Polymerisation von Ethylen unter Hochdruck gepruft. Das Ziel, den Initiatorverbrauch zu reduzieren und die Polymerisationstemperatur abzusenken, konnte ohne die Lewisbase mit Tkialkylaluminium allein erreicht werden.Von den untersuchten Tkialkylaluminiumverbindungen erwies sich das Tkiethylaluminium als effektivstes System. Seine Wirkung beruht auf der Beschleunigung des

Activation of the decomposition oftert-butyl peroxypivalate with trialkylaluminium compounds

“…The radical polymerisation of ethylene can be activated at very low temperatures by a combination of trialkylaluminium and Lewis bases 5) . At elevated temperatures, an addition of trialkylaluminium to the peroxide is sufficient to accelerate the polymerisation of ethylene 6) . The purpose of this study was to show that the activating effect of the trialkylaluminium compound is the result of an increase in the rate of decomposition of the peroxide.…”