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 s ilanolytic (PhSiH3, PhMeSiH2, Me2SiH2, Et2SiH2) chain transfer in the homog eneous polymerization and copolymerization of a variety of a-olefins. The r esult is several broad classes of silyl-capped and silyl-linked polyolefins which have been characterized by H-1/C-13/Si-29 NMR and IR spectroscopy as well as by GPC. "Single-site" Ziegler-Natta catalysts effect this chain tr ansfer with significant efficiency and scope. For [Me2Si(Me4C5)(BuN)-Bu-t]T iMe+B(C6F5)(4)(-)-mediated propylene polymerization, the mechanism of chain transfer is supported by the observation that M-n of the capped atactic po lypropylenes produced at constant [catalyst]. [PhSiH3], and [propylene] is inversely proportional to[PhSiH3]. Using the same catalyst, this process al so efficiently products silyl endcapped poly(l-hexene), ethylene + l-hexene copolymers, ethylene + styrene copolymers (both with high degrees of comon omer incorporation), and (at low temperatures) polyethylene. In the case of rac-C2H4(Ind)(2)TiMe+B(C6F5)(4)(-) + propylene and (Me5C5)TiMe2+B(C6F5)(4) (-) + styrene, PhH2Si-functionalized isotatic polypropylene and syndiotacti c polystyrene, respectively, are produced. Using 1, 4-disilabenzene and 1,3 ,5-trisilabenzene as chain-transfer agents in the presence of [Me2Si(Me4C5) (BuN)-Bu-1]TiMe+B(C6F5)(4)(-) + propylene, linear diblock and starlike atac tic polypropylene structures, respectively, are produced. In addition to pr imary silanes, secondary silanes (PhMeSiH2, Me2SiH2:, Et2SiH2) are efficien t and selective chain-transfer agents in this organotitanium-mediated polym erization. In the presence of [Me2Si(Me4C5)(BuN)-Bu-1]TiMe+B(C6F5)(4)(-) propylene (Me5C5)TiMe2+B(C6F5)(4)(-) + propylene, and (Me5C5)TiMe2+B(C6F5)( 4)(-) + styrene, PhMeHSi- or Me2HSi-capped atactic polypropylene and PhMeHS i-, Me2HSi-, or Et2HSi-capped syndiotactic polystyrene are produced, respec tively. Using PhH2Si-capped polypropylene as a chain-transfer agent, an ata ctic polypropylene-syndiotactic polystyrene AB block; copolymer is produced in the presence of (Me5C5)TiMe2+B(C6F5)(4)(-) + styrene.