Polymerization of MMA by oscillating zirconocene catalysts, diastereomeric zirconocene mixtures, and diastereospecific metallocene pairs
作者:Yalan Ning、Megan J. Cooney、Eugene Y.-X. Chen
DOI:10.1016/j.jorganchem.2005.01.070
日期:2005.12
Characteristics of methyl methacrylate (MMA) polymerization using oscillating zirconocene catalysts, (2-Ph-Ind)(2)ZrX2 (X = Cl, 1; X = Me, 2), mixtures of rac- and meso-zirconocene diastereomers, (SBI)ZrMe2 [3, SBI = Me2Si(Ind)(2)] and (EBI)ZrMe2 [4, EBI = C2H4(Ind)(2)], as well as diastereospecific metallocene pairs, rac-4/Cp2ZrMe2 (5) and rac-4/CGCTiMe(2) [6, CGC = MeSi(Me4C5)(t-BuN)], are reported. M MA 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(C6F5)(3) or 2/Ph3CB(C6F5)(4) is controlled and produces syndiotactic PMMA. Mixtures of diastereorneric ansa-zirconocenes 3 or 4 containing various rac/meso ratios, when activated with B(C6F5)(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. (c) 2005 Elsevier B.V. All rights reserved.