The polymerization of ethylene with a soluble titanium-aluminium complex

Abstract

The reaction between biscyclopentadienyl titanium dichloride and aluminium alkyls and alkyl chlorides has been examined by ESR spectroscopy, and by the abilities of the various resulting complexes to initiate the polymerization of ethylene at 1 atm and ambient temperature. In general, it is concluded that the active initiating species is a Ti(IV) complex, and not the paramagnetic Ti(III) complexes. Accordingly, the development of an ESR spectrum is accompanied by a fall off in initiating efficiency, decrease in polymerization rate and increased molecular weight of the polymers produced. The reduction of Ti(IV) to Ti(III) during the polymerization accounts for the fall in rate with conversion; addition of an oxidizing agent (1:2-dichloroethane) to the polymerization converts Ti(III) to Ti(IV), as observed by the disappearance of the ESR signal, and increases the efficiency of the polymerization. Block copolymers of ethylene with propylene and butadiene have been prepared with this initiator; the efficiency in producing blocks has been used to study the decomposition of the active sites by a first order reduction process.