Rationally designed hyperbranched azopolymer with temperature, photo and pH responsive behavior

Abstract

A new azobenzene-containing hyperbranched polymer, HPAzoAMAM-star-EG₃, was efficiently synthesized via two-step Michael addition polymerization. The proposed polymer could self-assemble into uniform large compound micelles (LCMs) that show temperature, photo and pH responsiveness. The LCMs turned into pancake-like platelets when cooled to ca. 20 °C and their spherical morphology was restored at temperatures higher than 30 °C. Upon irradiation with linear polarized light (LPL), the LCMs were elongated into short spindles. The photo-isomerization rate could be accelerated by loading silver nanoparticles (SNPs) into the LCMs via direct reduction. Moreover, the LCMs broke down into a much smaller size when the pH value was less than a critical point, ca. 3.90, whereas they remained stable at higher pH values. The combined advantages of the facile synthesis, hyperbranched structure, uniform morphology of assembly and multi-responsiveness endow the polymer with promising potential for applications in controlled release and smart deformable micro/nanostructures.