Chlorolanthanocene-dialkylmagnesium systems for styrene bulk polymerization and styrene-ethylene block copolymerization

Abstract

The bulk polymerization of styrene has been investigated at 105°C in the presence of exclusively dialkylmagnesium or combination of chlorolanthanocene and dialkylmagnesium. In the presence of butylethylmagnesium or n,s-dibutylmagnesium, styrene polymerization proceeds via thermal self-initiation, but is accompanied by a reversible transfer to dialkylmagnesiums to yield in turn oligostyrylmagnesium species; the latter are finally hydrolysed to oligostyrenes with M n = 300-1500 and M w / M n = 2.0-2.8. The analysis of the oligostyrenes by MALDI-TOF mass spectrometry establishes the presence of ethyl and butyl headgroups. consistent with the transfer process. When the dialkylmagnesium is combined with a lanthanocene such as (C 5 Me 5 ) 2 NdCl 2 Li(OEt 2 ) 2 (1), an increase in activity is obtained which is ascribed to addinonal styrene polymerization initiated by in situ generated alkylthydride)lanthanocene species. The influence of varions reaction parameters on the performance of this system has been investigated. The oligostyrenes (M m = 500-9000) produced under optimum conditions have a relatively narrow molar mass distribution (M w /M n = 1.20-1.40) which can be explained in terms of an efficient transfer between the chain-growing lanthanide and the oligostyrylmagnesium spectes. The MALDI-TOF mass spectra of the oligostyrenes produced with various dialkyimagnesium-lanthanocene combinations gives an insight into the initiation mechanism. Fanally, the combination of butylethylmagnesium and Cp * 2 NdCl 2 Li(OEt 2 ) 2 has been used to achieve (styrene-co-athylene) block copolymers.