Synthesis and characterization of well-defined thermo- and light-responsive diblock copolymers by atom transfer radical polymerization and click chemistry

Abstract

We synthesized a series of well-defined, stimuli-responsive diblock copolymers composed of poly(N-isopropylacrylamide) and poly(6-[4-(4-methoxyphenylazo)phenoxy]hexyl methacrylate) by atom transfer radical polymerization and click chemistry. The diblock copolymers were then characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography. When the azobenzene content reached 4.5 mol%, the diblock copolymer became insoluble in water. The aqueous solutions of the polymers exhibited a lower critical solution temperature (LCST) that depended on the amount of incorporated azobenzene. Higher LCSTs were observed after UV irradiation, with a maximum difference of 4.1 °C for the copolymer containing 1.4 mol% azobenzene groups. The photochemical properties of the polymer were also studied by UV-vis spectroscopy.