Organolanthanide-Mediated Silanolytic Chain Transfer Processes. Scope and Mechanism of Single Reactor Catalytic Routes to Silapolyolefins

This paper reports efficient and selective silanolytic (PhSiH 3, n -BuSiH 3, C 6 H 5 CH 2 SiH 3 ) chain transfer in organolanthanide-catalyzed homogeneous ethylene polymerization and ethylene copolymerization with several α-olefins. The result is a series of silyl-capped polyolefins which have been characterized by 1 H/ 13 C NMR and IR spectroscopy as well as by GPC. In [(Me 5 C 5 ) 2 LnH] 2 /[Me 2 Si(Me 4 C 5 ) 2 LnH] 2 -mediated ethylene homopolymerization and ethylene copolymerization, both primary arylsilanes (PhSiH 3 ) and alkylsilanes ( n -BuSiH 3, C 6 H 5 CH 2 SiH 3 ) function as efficient chain-transfer agents. In the case of ethylene polymerization mediated by [(Me 5 C 5 ) 2 SmH] 2, the mechanism of chain transfer is supported by the observation that M n of the capped polyethylenes formed at constant [catalyst], [PhSiH 3 ], [ethylene] is inversely proportional to [PhSiH 3 ]. Using silane-activated Me 2 Si(Me 4 C 5 ) 2 LnCH(SiMe 3 ) 2 precatalysts, this chain-transfer process also efficiently produces silyl-endcapped ethylene + 1-hexene copolymers and ethylene + styrene copolymers.