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

Full Paper: The bulk polymerization of styrene has been investigated at 105 degrees C in the presence of exclusively dialkylmagnesium or combination o f chlorolanthanocene and dialkylmagnesium. In the presence of butylethylmag nesium or n,s-dibutylmagnesium, styrene polymerization proceeds via thermal self-initiation, but is accompanied by a reversible transfer to dialkylmag nesiums to yield in turn oligostyrylmagnesium species; the latter are final ly hydrolysed to oligostyrenes by MALDI-TOF mass spectrometry establishes t he presence of ethyl and butyl headgroups, consistent with the transfer pro cess. When the dialkylmagnesium is combined with a lanthanocene such as (C5 Me5)(2)NdCl2Li(OEt2)(2) (1), an increase in activity is obtained which is a scribed to additional styrene polymerization initiated by in situ generated alkyl(hydride)lanthanocene species. The influence of various reaction para meters on the performance of this system has been investigated. The oligost yrenes ((M) over bar(n) = 500-9000) produced under optimum conditions have a relatively narrow molar mass distribution ((M) over bar(w)/(M) over bar(n ) = 1.20-1.40) which can be explained in terms of an efficient transfer bet ween the chain-growing lanthanide and the oligostyrylmagnesium species. The MALDI-TOF mass spectra of the oligostyrenes produced with various dialkylm agnesium-lanthanocene combinations gives an insight into the initiation mec hanism. Finally, the combination of butylethylmagnesium and Cp-2*NdCl2Li(OE t2)(2) has been used to achieve (styrene-co-ethylene) block copolymers.