Vesicular and micellar self-assembly of stimuli-responsive poly(N-isopropyl acrylamide-b-9-anthracene methyl methacrylate) amphiphilic diblock copolymers

Abstract

Dually responsive amphiphilic diblock copolymers consisting of hydrophilic poly(N-isopropyl acrylamide) [poly(NIPAAm)] and hydrophobic poly(9-anthracene methyl methacrylate) were synthesized by reversible addition fragmentation chain-transfer (RAFT) polymerization with 3-(benzyl sulfanyl thiocarbonyl sulfanyl) propionic acid as a chain-transfer agent. In the first step, the poly(NIPAAm) chain was grown to make a macro-RAFT agent, and in the second step, the chain was extended by hydrophobic 9-anthryl methyl methacrylate to yield amphiphilic poly(N-isopropyl acrylamide-b-9-anthracene methyl methacrylate) block copolymers. The formation of copolymers with three different hydrophobic block lengths and a fixed hydrophilic block was confirmed from their molecular weights. The self-assembly of these copolymers was studied through the determination of the lower critical solution temperature and critical micelle concentration of the copolymers in aqueous solution. The self-assembled block copolymers displayed vesicular morphology in the case of the small hydrophobic chain, but the morphology gradually turned into a micellar type when the hydrophobic chain length was increased. The variations in the length and chemical composition of the blocks allowed the tuning of the block copolymer responsiveness toward both the pH and temperature. The resulting self-assembled structures underwent thermally induced and pH-induced morphological transitions from vesicles to micelles and vice versa in aqueous solution. These dually responsive amphiphilic diblock copolymers have potential applications in the encapsulation of both hydrophobic and hydrophilic drug molecules, as evidenced from the dye encapsulation studies. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46474.