One-Pot Synthesis of Polyethylene-Based Block Copolymers <i>via</i> a Dual Polymerization Pathway
Yajun Zhao, Jin Chul Jung, Kyoko Nozaki
Abstract
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.