POLYMERIZATION OF METHYL-METHACRYLATE WITH NON-BRIDGED ZIRCONOCENE CATALYSTS

Four non-bridged dimethylzirconocene complexes, i.e., bis(eta(5)-cyclo pentadienyl)dimethylzirconium (1), (eta(5)-cyclopentadienyl) (eta(5)-f luorenyl)dimethylzirconium (2), bis(eta(5)-indenyl)dimethylzirconium ( 3) and a(5)-pentamethylcyclopentadienyl)dimethylzirconium (4) were syn thesized and used as a catalyst for the methyl methacrylate polymeriza tion combined with triphenylmethyl tetrakis(pentafluorophenyl)borate i n the presence of ZnEt2 or Al(i-Bu)(3). The catalyst activity strongly depends on the zirconocene compound and decreases in the order 2 > 1 > 3 >> 4. The polymerization proceeds in a living manner when 1 and 2 are used combined with ZnEt2. On the other hand, stereoregularities of the resulting polymers are independent of the zirconocene compound, a nd syndiotactic-rich polymers are formed by a chain-end controlled mec hanism.