Multitunable Thermoresponsive and Aggregation Behaviors of Linear and Cyclic Polyacrylamide Copolymers Comprising Heterofunctional Y Junctions

The incorporation of asymmetric Y junctions into thermoresponsive polymers allows access to hierarchical self-assembly, and self-assembly of cyclic polymers can further amplify the topology effect. At present, systematic insights into the influence of Y junctions on physicochemical properties remain at the early stage. A diversity of linear and cyclic polyacrylamide copolymers with substituent-variable Y junctions are designed to reveal the effects of topology, chain length, composition, concentration, and temperature. With the increasing size of substituents, copolymer aqueous solutions gradually shift from dual upper and lower critical solution temperatures (UCST/LCST) to a single LCST until the lack of phase transition. The LCST can be elevated by introduction of a cyclic architecture, longer polymer chain, and smaller substituent. Owing to the changes in degree of hydration of subunits, heat can induce sphere-vesicle-nanosheet-nanoribbon-sphere (linear copolymer) and sphere-nanosheet-nanoribbon (cyclic copolymer) transitions. In addition, the cyclization effect is also reflected in cooperative hydration of distinct subunits upon heating, higher ceiling temperatures to form stable lamellae, and more pronounced hysteresis of the turbidity curve upon cooling. This research using Y junction bearing thermoresponsive copolymers may provide a promising platform to achieve on-demand phase transitions and nanostructures.

Automated summary

The incorporation of asymmetric Y junctions in thermoresponsive polymers allows for hierarchical self-assembly, and self-assembly of cyclic polymers can amplify topology effects. Research on the influence of Y junctions on physicochemical properties is still in the early stages, with a variety of copolymers designed to explore the effects of topology, chain length, composition, concentration, and temperature.