Thermo- and pH-sensitive polyethylene-based diblock and triblock copolymers: synthesis and self-assembly in aqueous solution

Abstract

Well-defined polyethylene-block-poly(N-isopropylacrylamide) (PE-b-PNIPAM) and polyethylene-block-poly(N-isopropylacrylamide)-block-poly(2-vinylpyridine) (PE-b-PNIPAM-b-P2VP) were successfully synthesized by a combination of coordination chain transfer polymerization (CCTP) with reversible addition-fragmentation chain transfer (RAFT) polymerization in a “living”/controlled manner. Hydroxyl-terminated polyethylene (PE–OH) was firstly prepared by in situoxidation of polymer produced by CCTP with bis(imino)pyridine iron/MAO/ZnEt2 catalytic system. After an esterification of PE–OH with S-1-dodecyl-S′-(α,α′-dimethyl-α′′-acetate) trithiocarbonate, trithiocarbonate-terminated polyethylene (PE–trithiocarbonate) was obtained in high yield and used as a macromolecular chain transfer agent (macro-CTA) for RAFT polymerizations of NIPAM and 2VP. The results confirm that the tandem polymerization is an effective approach for synthesizing polyolefin-based amphiphiles. The amphiphilic block copolymers in aqueous solution can self-assemble into a nanodisk-like micelle containing a thin crystalline PE lamella domain between layers of the hydrophilic blocks. Dynamic light scattering (DLS) analyses demonstrated the thermo-responsive property of diblock copolymer PE-b-PNIPAM and double thermo- and pH-responsive properties of triblock copolymer PE-b-PNIPAM-b-P2VP.