Synthesis of well-defined amphiphilic branched polyethylene-graft-poly (N-isopropylacrylamide) copolymers by coordination copolymerization in tandem with RAFT polymerization and their self-assembled vesicles

Abstract

A tandem synthetic strategy combining the metal catalyzed copolymerization of ethylene with trimethylsilyl-protected 10-undecen-1-ol and RAFT polymerization was successfully used to prepare well-defined branched polyethylene-graft-poly(N-isopropylacrylamide) copolymers (BPE-g-PNIPAM). The branched PEs containing multiple hydroxyls (BPE–(OH)n) were firstly synthesized by the copolymerization of ethylene with trimethylsilyl-protected 10-undecen-1-ol using a pyridine–amine nickel catalyst in a controlled fashion (Mw/Mn ∼ 1.2). Macro-chain transfer agents (macro-CTAs) for a subsequent polymerization of N-isopropylacrylamide were quantitatively obtained by an esterification reaction of BPE–(OH)n with S-1-dodecyl-S′-(α,α′-dimethyl-α′′-acetate) trithiocarbonate. Chain extensions by a RAFT polymerization were successfully achieved to afford BPE-g-PNIPAM graft copolymers with narrow polydispersities of ∼1.2. Investigations of the self-assembly behavior of the obtained BPE-g-PNIPAM graft copolymers in water by means of TEM, AFM and laser light scattering confirm that the amphiphilic graft copolymers form supramolecular vesicles with average diameters of 170–190 nm in aqueous solution. Dynamic light scattering (DLS) measurements demonstrate that the polymer vesicles are thermo-sensitive and show a distinctive two-stage response from 20 to 32 °C.