One-Pot Synthesis of Polyethylene-Based Block Copolymers via a Dual Polymerization Pathway.

Polyethylene-poly(methyl acrylate) multiblock copolymers were obtained using a catalyst system consisting of a pentamethylcyclopentadienyl cobalt complex (CoIII(η5-C5H5)P(OMe)3I2) and iso-butyl modified methylaluminoxane (MMAO). As the chain-growth mechanism, the self-switching between organometallic-mediated radical polymerization (OMRP) and coordination-insertion polymerization (CIP) is suggested. As a possible polymerization mechanism, we propose that (1) the methyl and iso-butyl groups transfer from Al to Co and the single methyl acrylate (MA) unit insertion into the Me-Co and H-Co allows for the in situ formation of Co-C(COOMe) bonds as an initiator for OMRP of MA, (2) the migratory insertion of ethylene into Co-C(COOMe) bonds leads to the formation of an alkyl-Co species as active species for CIP of ethylene, and (3) MA insertion to the alkyl-Co to regenerate a Co-C(COOMe) bond. The architectures of copolymers were confirmed by various nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC), and size-exclusion chromatography (SEC) analyses.