Noncovalent and Dynamic Covalent Chemistry Strategies for Driving Thermoresponsive Phase Transition with Multistimuli and Controlled Encapsulation/Release

We report the development of multiresponsive thermally sensitive polymers through both supramolecular and reversible covalent strategies as well as their use in controlled encapsulation and release. Novel acylhydrazone-based dynamic covalent polymers displaying lower critical solution temperature (LCST) or upper critical solution temperature (UCST) were synthesized. A remarkable control over thermal phase transition can be tuned through multimodes, such as anions, cations, solvent, pH, and competing components. In particular, anion recognition allowed disassembly and thus led to a significant decrease of UCST in dimethyl sulfoxide, and the combination of anion and solvent effects offered additional handle for control. Moreover, the use of anions, cations, as well as pH change was employed for the modulation of LCST-type polymer in water. Furthermore, switching on/off thermoresponsiveness was readily achieved by dynamic covalent exchange. Mechanistic studies also shed light on stimuli-induced changes in aggregation behaviors. Finally, thermally controlled encapsulation and release of hydrophobic and hydrophilic dyes were realized with great repeatability and reversibility, respectively, showing potential in delivery and sensing. The results and strategies described should provide opportunities for many aspects, including dynamic assemblies, complex systems, and adaptive materials.