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)(t)BuN]TiMe+B(C6F5)4--mediated propylene polymerization, the mechanism of chain transfer is supported by the observation that M(n) 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) polyethylene. In the case of rac-C2H4(ind)2TiMe+B-(C6F5)4- + propylene and (Me5C5)TiMe2+B(C6F5)4- + styrene, PhH2Si-functionalized isotatic polypropylene and syndiotactic polystyrene, respectively, are produced. Using 1,4-disilabenzene and 1,3,5-trisilabenzene as chain-transfer agents in the presence of [Me2Si(Me4C5)1BuN]TiMe+B(C6F5)4- + propylene, linear diblock and starlike atactic polypropylene structures, respectively, are produced. In addition to primary silanes, secondary silanes (PhMeSiH2, Me2SiH2, Et2SiH2) are efficient and selective chain-transfer agents in this organotitanium-mediated polymerization. In the presence of [Me2Si(Me4C5)(t)BuN]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 PhMeHSi-, Me2HSi-, or Et2HSi-capped syndiotactic polystyrene are produced, respectively. Using PhH2Si-capped polypropylene as a chain-transfer agent, an atactic polypropylene-syndiotactic polystyrene AB block copolymer is produced in the presence of (Me5C5)TiMe2+B(C6F5)4- + styrene.
ASJC Scopus subject areas
- Colloid and Surface Chemistry