Synthesis and Thermoresponsive Behaviors of Thermo-, pH-, CO2- and Oxidation-Responsive Linear and Cyclic Graft Copolymers

Rational macromolecular design allows us to multiresponsive architectural polymers with a potential toward multipurpose applications. This study aims at synthesis and LCST-type thermoresponsive behaviors of multisensitive linear and cyclic graft copolymers with polyacrylamide backbone and hydrophilic PEG grafts. The cloud point could be tuned by many factors, and the effect of cyclization was confirmed by the elevated cloud point in H2O up to 12.8 degrees C under same conditions. The PEG-connecting Y junctions with dual amide, thioether, and tertiary amine groups allowed thermo-, solvent-, pH-, and CO2-switchable inter/intramolecular hydrogen bonding interactions and hence resulted in unusual solvent (H2O or D2O) and pH (about 6.8-8.5) dependent phase transition and irreversible CO2-responsive behavior. Meanwhile, the solution blending could lead to one or two phase transition(s) dependent on types and compositions of the blends. The meticulous introduction of multifunctional Y junctions into graft copolymers offers a versatile route to adjust multitunable thermoresponsive properties.