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

摘要

Full Paper: The bulk polymerization of styrene has been investigated at 105 degrees 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 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 (C5Me5)(2)NdCl2Li(OEt2)(2) (1), an increase in activity is obtained which is ascribed to additional styrene polymerization initiated by in situ generated alkyl(hydride)lanthanocene species. The influence of various reaction parameters on the performance of this system has been investigated. The oligostyrenes ((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 between the chain-growing lanthanide and the oligostyrylmagnesium species. The MALDI-TOF mass spectra of the oligostyrenes produced with various dialkylmagnesium-lanthanocene combinations gives an insight into the initiation mechanism. Finally, the combination of butylethylmagnesium and Cp-2*NdCl2Li(OEt2)(2) has been used to achieve (styrene-co-ethylene) block copolymers. [References: 58]