Preparation of an ethylene glycol-based block copolymer consisting of six different temperature-responsive blocks

Abstract

An ethylene glycol-based hexa-block copolymer with six different temperature-responsive blocks was prepared via a reversible addition-fragmentation chain transfer (RAFT) polymerization. 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA) were selected as the ethylene glycol-based monomers. Each block of the hexa-block copolymer has a different OEGMA content and thus exhibits a different lower critical solution temperature (LCST). The structures of the block copolymers are similar to gradient copolymers. The molecular weights of the copolymers increased with the number of blocks (first block (P(MEO2MA)): 2800 g/mol, di-block copolymer: 7400 g/mol, tri-block copolymer: 12,000 g/mol, tetra-block copolymer: 18,500 g/mol, penta-block copolymer: 26,800 g/mol, and hexa-block copolymer: 40,400 g/mol) with relatively narrow molecular weight distributions (1.18–1.42). Each block exhibits a different LCST in aqueous solution owing to their different OEGMA contents. To the best of our knowledge, this is the first report of a block copolymer containing more than four types of temperature-responsive blocks. The temperature-responsive properties of the prepared block copolymers were investigated by UV-vis spectroscopy, micro-differential scanning calorimetry, and scanning electron microscopy. An ethylene glycol-based hexa-block copolymer with six different temperature-responsive blocks was prepared via a reversible addition-fragmentation chain transfer (RAFT) polymerization. 2-(2-Methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA) were selected as the ethylene glycol-based monomers. Each block exhibits a different LCST in aqueous solution owing to their different OEGMA contents.