Abstract
Polymerization of methyl methacrylate (MMA) was conducted with the catalyst systems of rac-Et(Ind) 2 Zr(CH 3 ) 2 /Ph 3 CB(C 6 F 5 ) 4 , rac-Et(IndH 4 ) 2 Zr(CH 3 ) 2 /Ph 3 CB(C 6 F 5 ) 4 , and rac-Me 2 Si(Ind) 2 Zr(CH 5 ) 2 /Ph 3 CB(C 6 F 5 ) 4 . These catalysts only were found to be inactive. However, the addition of suitable Lewis acids like alkylzinc and alkylaluminum compounds gave highly isotactic PMMA. The isotactic pentad [mmmm] in PMMA as well as the propagation rate constant (k p ) depended significantly upon the zirconocene compounds. Both the microstructure ([mmmm]) and propagation rate constant (k p ) increased in the following order. Me 2 Si(Ind) 2 CH 2 CH 3 > (CH 2 ) 3 CH 3 . When the polymerization was initiated by the rac-Et(Ind) 2 Zr(CH 3 ) 2 /Ph 3 CB(C 6 F 5 ) 4 /Zn(C 2 H 4 CH=CH 2 ) 2 catalyst system at 0°C in toluene, the molecular weight of PMMA increased in proportion to the conversion of MMA. The increase of temperature from 0 to 80°C caused a decrease in isotactic pentad content by approximately 10%. The isotactic polymerization of MMA was revealed to proceed by an enantiomorphic site-controlled mechanism
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