Design of a New LCST Copolymer Based on Hydrogen Bonding Regulation

Hydrogen bonding is one of the key factors determining polymer thermoresponsiveness. For instance, in Upper Critical Solution Temperature (UCST) poly(acrylamide- co -acrylonitrile) (P(AAm- co -AN)) aqueous solution, hydrogen bonding between AAm units is the primary driving force for the UCST transition. If the hydrogen atoms on the amide group are substituted, the absence of hydrogen donors may influence the thermoresponsive behavior and could even induce a shift from Upper Critical Solution Temperature to Lower Critical Solution Temperature (LCST). In this work, poly(N,N-dimethylacrylamide- co -acrylonitrile) (P(DMAA- co -AN)) was synthesized. Because the copolymer contains only hydrogen acceptors, hydrogen bonding cannot form between polymer structural units in aqueous solution. Thus, only polymer–water hydrogen bonding is formed. P(DMAA- co -AN) exhibits typical LCST-type thermoresponsive behavior, which confirms the proposed hypothesis. The copolymers exhibited cloud points in the ambient temperature range of 19°C−68°C by varying the composition ratio of DMAA and AN. P(DMAA- co -AN) exhibits thermoresponsive, salt- and pH-responsive behaviors, which provide potential applications in the fields of biomedicine and petrochemical engineering. In this work, hydrogen bonding interactions were regulated by simply replacing hydrogen atoms on the functional groups, thus inducing changes in the thermoresponsiveness of the copolymer. It offers valuable insights for the design of novel thermoresponsive polymers.