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Stereoblock Copolymerization of Propylene and Methyl Methacrylate with Single-Site Metallocene Catalysts

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Abstract

Sequential stereoblock copolymerization of propylene (P) and methyl methacrylate (MMA) using Group IV single-site metallocene catalysts efficiently produces PP-b-PMMA stereodiblock copolymers. When activated with B(C6F5)3, C2-symmetric rac-Et(Ind)2ZrMe2 yields isotactic-PP-b-isotactic-PMMA diblock copolymer, whereas Cs-symmetric Me2Si(C5Me4)(tBuN)TiMe2 affords atactic-PP-b-syndiotactic-PMMA diblock copolymer. In the copolymerization catalyzed by the C2-symmetric catalyst, a very small amount of PMMA homopolymer formed can be removed from the copolymer by extracting the bulk polymer product with boiling methylene chloride. However, separation of isotactic PP formed if any from the copolymer product approves very difficult, due to very similar solubility between the diblock copolymer and isotactic PP homopolymer in various high-boiling chlorinated solvents. On the other hand, in the copolymerization catalyzed by the Cs-symmetric catalyst, both PMMA and atactic PP homopolymers formed in small weight fractions during the copolymerization can be successfully removed from the predominant copolymer product by solvent extraction using boiling heptane. After successful removal of both homopolymers, for example, an atactic-PP-b-syndiotactic-PMMA diblock copolymer has high molecular weight (Mn = 21 100), narrow molecular weight distribution (PDI = 1.08), high PMMA incorporation (33.8 mol-% of PMMA), and moderate syndiotacticity for the PMMA block ([rr] ≈ 80%). Furthermore, the comonomer composition in the copolymer can be controlled by the time for propylene polymerization and the conversion of MMA. A pronounced activator effect is observed; when the same Cs-symmetric catalyst is activated with Ph3CB(C6F5)4, formation of homopolymers is predominated.

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