Single-chain crosslinked star polymers via intramolecular crosslinking of self-folding amphiphilic copolymers in water

Abstract

Single-chain crosslinked star polymers with multiple hydrophilic short arms and a hydrophobic core were created as novel microgel star polymers of single polymer chains. The synthetic process involves the intramolecular crosslinking of self-folding amphiphilic random copolymers in water. For this process, amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic olefin pendants were synthesized by ruthenium-catalyzed living radical copolymerization of PEG methyl ether methacrylate, dodecyl methacrylate and hydroxyl-functionalized methacrylates, and the in situ or postesterification of the hydroxyl pendants of the resulting copolymers with methacryloyl chloride. The olefin-bearing copolymers with 20-40 mol% hydrophobic units efficiently self-folded because of hydrophobic interactions in water. These folded structures were then crosslinked intramolecularly using a free radical initiator or a ruthenium catalyst to selectively yield single-chain crosslinked star polymers, whereas a counterpart containing 50 mol% hydrophobic units induced bimolecular aggregation in water to give double-chain crosslinked star polymers. The primary structure of the star polymers can be precisely controlled with random copolymer precursors. Owing to the PEG arm units, the star polymers further showed thermosensitive solubility in water.