Controllable Preparation of Branched Polyolefins with Various Microstructural Units via Chain-walking Ethylene and Pentene Polymerizations

Branched polyolefins with controllable topology structures were generated from the chain-walking (co)polymerizations of ethylene, 1-pentene (1P) and 2-pentene (2P) using Brookhart-type a -diimine Ni(II)-based catalysts possessing different para -substituted groups, {[(4-R-2-Et-6-Me-C 6 H 2 N = C) 2 Nap]NiBr 2 , Nap: 1,8-naphthdiyl; R = CHMePh, Ni1 ; R = Ph, Ni2 ; R = H, Ni3 }. The X-ray diffraction analysis demonstrated that the crystalline structure of Ni1 ’ is in centrosymmetric dimer structure mode with the bimetallic Ni center connected by two bromide bridges. The para-sec -phenethyl moiety in the catalyst Ni1 obviously improved its catalytic performance and thermal stability in the ethylene polymerization. The Ni1 /Et 2 AlCl system showed great catalytic activities (up to 7.73×10 6 g·mol −1 ·h −1 ) and achieved polyethylene (PE) with alkyl chains, including Me, Et, n -Pr, n -Bu, sec -Bu branches and longer chains (Lg). Compared with the 1-pentene polymerization, this catalyst system successfully mediated the polymerization of 2P to give highly branched polymers with approximately 195 branches/1000C possessing Me, Et, and n -Pr branches and a long methylene sequence due to the monomer isomerization. The Et branches derived from 2,3-insertion is slightly less than the sum of Me and n -Pr branches derived from 3,2-insertion, indicating that the 3,2-insertion mode is a slightly favorable pathway in the polymerization of 2P.