【摘 要】
：
Steric bulk plays a significantly paramount role in late transition metal promoted olefin (co)polymerization in terms of polymer mo-lecular weight and catalyst thermal stability.Numerous sterically encumbered nickel and palladium catalysts have been devel
【机 构】
：
State Key Laboratory of Polymer Physics and Chemistry,Changchun Institute of Applied Chemistry,Chine
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Steric bulk plays a significantly paramount role in late transition metal promoted olefin (co)polymerization in terms of polymer mo-lecular weight and catalyst thermal stability.Numerous sterically encumbered nickel and palladium catalysts have been developed,but they are usually uni-directional.In this contribution,from a bi-directional side the distinctive horizontally and vertically concerted steric strategy was well-developed and applied to α-diimine nickel catalysts.In ethylene polymerization,the increase of vertically ste-ric bulk (H,Ph,Biph) led to an enhanced polymer molecular weight,a slightly ascended branching density;likewise increasing hori-zontally steric bulk (Ph,Nap,Ant) further resulted in the increase of polymer molecular weight and branching density.As a result,in sharp contrast to Ni1(H) without steric bulk,Ni5(Ant) with horizontally and vertically concerted steric bulk was thermally stable,showed very high activities at a level of 107 g·mol-1·h-1,and produced polyethylenes with the highest molecular weight of 518.8 × 104 g·mol-1 and the broader range of branching density from 2.4/1000C to 27.8/1000C.In the copolymerization of ethylene with methyl 10-undecenoate,Ni5(Ant) also provided the highest copolymer molecular weight but gave the lowest incorporation of co-monomer.This work sheds light on the steric effect on olefln (co)polymerization.
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