9419305 Chung A broad range of functional polymers and graft copolymers, with polypropylene (PP), ethylene-propylene copolymers, and polyisobutylene backbones, have been synthesized by using a borane approach. Most of them would be very difficult to obtain by other existing methods. The key advantages of the borane approach are (a) the stability of borane groups to transition metal catalysts, such as Ziegler-Natta and metathesis catalysts, (b) the solubility of borane groups in the hydrocarbon solvents used in the polymerization reactions (both are essential to ensure the effective incorporation of borane groups in polyolefins under conventional reaction conditions) and (c) the versatility of borane groups which can be transformed to a remarkable variety of functionalities. In addition, the borane groups in polymer can be selectively auto-oxidized to polymeric radicals, which are then used as a active sites for graft polymerizations. A broad range of polyolefin graft copolymers, with polyolefin backbone and functional polymer side chains, have thus been obtained. The successful results in the borane approach will now be used in four related areas: (1) "living" radical polymerization using oxidation adducts of borane moieties as the initiators; (2) a synthetic route to prepare borane-group terminated polyethylene (PE) and polypropylene by using Ziegler-Natta catalysts and borane chain transfer agents; (3) the utilization of borane-terminated polyolefins to prepare diblock copolymers that have a polyolefin block, such as PE and PP, and a functional polymer block; (4) the extension of the functionalization chemistry to metallocene "single- site" catalysts which will allow us to effectively incorporate borane groups in polyethylene. The resulting linear low-density polyethylene with various functional groups, such as -OH, -NH2 and halides, will be a both scientifically interesting and potentially commercially important material. %%% Overall, the goal is not only to extend the borane approach to broader polymer compositions and structures of functionalized polyolefins, but also to widen the role of borane reagents in polymer chemistry. These uses of borane reagents in polymers may provide us with new tools to control polymerization processes and to obtain polymer structures which can not be obtained by other existing methods.
