Synthesis of block and graft copolymers with linear polyethylene segments by combination of degenerative transfer coordination polymerization and atom transfer radical polymerization

Block and graft copolymers with polyacrylate and linear polyethylene segments were synthesized through a combination of degenerative transfer (DT) ethylene polymerization and atom transfer radical polymerization (ATRP). DT coordination polymerization was mediated by a bis(imino)-pyridineiron/diethylzinc binary catalyst system activated by MAO and was studied at various temperatures. The catalyst system achieved a well-controlled DT coordination polymerization of ethylene, resulting in low-polydispersity polyethylene with high chain end functionality. The Zn-terminated polyethylene prepared by DT coordination polymerization was oxidized using dry air, followed by hydrolysis to provide a monohydroxy-terminated polyethylene (PE-OH). The degree of ethylene polymerization (DP similar to 20) and the chain end functionality (similar to 80%) of PE-OH were determined by H-1 NMR. The PE-OH was converted into a polyethylene alpha-bromoisobutyrate macroinitiator (PE-MI), and ATRP of n-butyl acrylate and tert-butyl acrylate was successfully conducted from the PE-MI to produce well-defined block copolymers. A PE-block-PnBA copolymer (M-n = 10100, M-w/M-n = 1.16 with 7.4 wt % PE segment) and a PE-block-PtBA copolymer (M-n = 11000, M-w/M-n = 1.16 with 6.8 wt % PE segment) were obtained successfully. The alpha-bromoisobutyrate/PE-MI was dehydrobrominated to form a polyethylene macromonomer with a terminal alpha-methacrylate group (PE-MM). A grafting-through ATRP was performed with the PE-MM and either n-butyl acrylate or tert-butyl acrylate to form well-defined PnBA-graft-PE and PtBA-graft-PE copolymers. Molecular structures were determined by H-1 NMR and GPC analysis. The PtBA-graft-PE was hydrolyzed yielding PAA-graft-PE with 90% carboxylic acid functionality. DSC analysis of the graft copolymers indicated two separate glass transitions, suggesting phase-separated morphology.