Synthesis and multi-tunable thermoresponsive behaviors of hyperbranched Y-junction-bearing copolymers

Chain architecture and chemical composition can play crucial roles in affecting thermoresponsive behaviors. To enrich molecular engineering of hyperbranched polymers and reveal the topology effect, thermo/pH-responsive hyperbranched Y-junction-bearing polymers (HYJPs) comprising 2-(N,N-dimethylamino)ethyl methacrylate and N-(1-(pyrrolidine-1-carbonyl)hydroxyalkoxycarbonylethylthioethyl) methacrylamide units are designed in this study. The increase of chain length of hydroxyalkyl groups endowed HYJP aqueous solutions with “on/off” LCST transition, decreased cloud point (T_c), and shape shift of copolymer assemblies from spheres to mixed nanostructures and vesicles, revealing the pivotal role of chemical composition. With increasing pH, T_c was usually liable to exhibit the evolution trend of first decreasing and then increasing due to improved hydrophilicity resulting from hydrolysis of ester groups. Compared with linear analogues, HYJPs in water showed distinct nano-object shape, lowered T_c and enhanced fluorescence intensity, revealing pronounced topology effect. Sphere/vesicle-to-nanoribbon/lamella transitions occurred during thermally induced self-assembly, and the formation of nanoribbons and lamellae led to elevated fluorescence intensity, corresponding to morphology transition enhanced emissions. With the incorporation of asymmetric heterofunctional Y junctions, the initial temperatures for varying transmittance, nano-object size and fluorescence emission were usually distinct due to complex conformational adjustment upon heating. The success of this study underlies multi-tunable properties and promising applications of HYJPs.