Silicon-Modified Ziegler−Natta Polymerization. Catalytic Approaches to Silyl-Capped and Silyl-Linked Polyolefins Using 'Single-Site' Cationic Ziegler−Natta Catalysts

This contribution reports efficient and selective organotitanium-mediated silanolytic (PhSiH3, PhMeSiH2, Me2SiH2, Et2SiH2) chain transfer in the homogeneous polymerization and copolymerization of a variety of α-olefins. The result is several broad classes of silyl-capped and silyl-linked polyolefins which have been characterized by 1H/13C/29Si NMR and IR spectroscopy as well as by GPC. “Single-site” Ziegler−Natta catalysts effect this chain transfer with significant efficiency and scope. For [Me2Si(Me4C5)tBuN]TiMe+B(C6F5)4--mediated propylene polymerization, the mechanism of chain transfer is supported by the observation that Mn of the capped atactic polypropylenes produced at constant [catalyst], [PhSiH3], and [propylene] is inversely proportional to [PhSiH3]. Using the same catalyst, this process also efficiently produces silyl endcapped poly(1-hexene), ethylene + 1-hexene copolymers, ethylene + styrene copolymers (both with high degrees of comonomer incorporation), and (at low temperatures) polyethylen...