Polymerization of MMA by oscillating zirconocene catalysts, diastereomeric zirconocene mixtures, and diastereospecific metallocene pairs

Abstract

Characteristics of methyl methacrylate (MMA) polymerization using oscillating zirconocene catalysts, (2-Ph-Ind) 2ZrX 2 (X = Cl, 1; X = Me, 2), mixtures of rac- and meso-zirconocene diastereomers, (SBI)ZrMe 2 [ 3, SBI = Me 2Si(Ind) 2] and (EBI)ZrMe 2 [ 4, EBI = C 2H 4(Ind) 2], as well as diastereospecific metallocene pairs, rac- 4/Cp 2ZrMe 2 ( 5) and rac- 4/CGCTiMe 2 [ 6, CGC = Me 2Si(Me 4C 5)( t-BuN)], are reported. MMA polymerization using the chloride catalyst precursor 1 activated with a large excess of the modified methyl aluminoxane is sluggish, uncontrolled, and produces atactic PMMA. On the other hand, the polymerization by a 2/1 ratio of 2/B(C 6F 5) 3 or 2/Ph 3CB(C 6F 5) 4 is controlled and produces syndiotactic PMMA. Mixtures of diastereomeric ansa-zirconocenes 3 or 4 containing various rac/ meso ratios, when activated with B(C 6F 5) 3, yield bimodal PMMA; this behavior is attributed to the meso-diastereomer that, in its pure form, affords bimodal, syndio-rich atactic PMMA. For MMA polymerization using diastereospecific metallocene pairs, rac- 4/ 5 and rac- 4/ 6, the isospecific catalyst site dominates the polymerization events under the conditions employed in this study, and the aspecific and syndiospecific sites are largely nonproductive, thereby forming only highly isotactic PMMA.