The catalytic activity in the polymerization of styrene has been examined using commercially available simple rare earth metal compounds such as Sm(OiPr) 3 , Sm(acac) 3 , Sm(OCOMe) 3 , SmI 2 (THF) 2 or SmCl 3 coupled with Et 3 Al or methylaluminoxane (MAO). Among these compounds, the Sm(OiPr) 3 /AlEt 3 system shows the highest catalytic activity, especially in the presence of a minor amount of toluene at 60°C. The random copolymerization of styrene with methyl methacrylate suggests that the present polymerization proceeds with a radical polymerization mechanism. (C 5 Me 5 )SmCl 3 Na(THF) and (C 5 Me 5 )SmCl 3 Li(THF) systems exhibit relatively low catalytic activity, even in the presence of AlEt 3 .

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