Thermoresponsive Polymers with Aqueous LCST and/or UCST through Postpolymerization Modification

摘要

Thermoresponsive polymers with aqueous lower critical solution temperature (LCST) and/or upper critical solution temperature (UCST) are of a wider academic interest and also have promising applications in many areas. However, not many types of polymers with a UCST in water are well known. Postpolymerization modification is a versatile technique for synthesizing functional polymers. Herein, novel thermoresponsive polymers with UCST and/or LCST were prepared through postpolymerization modification. Given that strong intermolecular interactions are necessary in order to realise polymers with aqueous UCSTs, amide-functional (co)polymers were firstly investigated through postpolymerization modification of the activated ester poly(pentafluorophenyl acrylate) (pPFPA) with amines including ammonia and amide derivatives of amino acids. While it was not a promising route toward thermoresponsive polymers with UCST in water, novel (co)polymers with aqueous LCSTs and a remarkable self-association of (co)polymers in the dry state were found. Next, zwitterionic (co)polymers were investigated with the goal of producing polymers with tuneable UCST transitions in water. Initially, different synthetic techniques were compared, and postpolymerization modification of pPFPA with sulfobetaine-functional amines was identified as a very versatile method to tune the UCST behaviour by incorporation of hydrophobic comonomer units. As a consequence, a range of novel UCST systems including such with UCST under physiologically relevant NaCl concentrations were prepared and characterised. In addition to pPFPA, poly(2-vinyl-4,4-dimethylazlactone) (pVDMA) was used as a less investigated platform to prepare thermoresponsive polymers, and a range of novel VDMA-derived (co)polymers with tuneable aqueous LCST behaviour were successfully synthesized through postpolymerization modification of pVDMA with different amines. Based on the previous experience with sulfobetaine-functional amines, in the final project, novel VDMA-derived polymers with aqueous UCST were identified and studied, and copolymers with both LCST and UCST in water were designed and prepared through postpolymerization modification of pVDMA with sulfobetaine-functional amines and tetrahydrofurfurylamine. In summary, these studies have made a strong contribution to the field of novel thermoresponsive polymers and especially the ease of preparing zwitterionic copolymer, and UCST or UCST and LCST is expected to be significant in the wider scientific community.