Synthesis and Phase Transition Study of Copolymer Poly(N-vinylpyrrolidone-co-diacetone acrylamide) with tailored LCST over a wide temperature range

Polymers with lower critical solution temperature (LCST) had broad application prospects in biomedicine and drug delivery. The copolymer poly(N-vinylpyrrolidone-co-diacetone acrylamide) (P(NVP-co-DAAM)) was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinylpyrrolidone (NVP) and diacetone acrylamide (DAAM). Ultraviolet transmittance was utilized to investigate its solution behavior. The results showed that by adjusting molar ratio of two monomers, the lower critical solution temperature (LCST) of the copolymer could be modulated for 12.0–59.9 °C. Variable-temperature Fourier transform infrared spectroscopy examined the interactions between the copolymer and water molecules. The results indicated that the hydroxyl absorption peak of the solvent water molecules exhibited blue-shift with rising temperature, indicating weakening interactions between copolymer and water molecules. Two-dimensional infrared correlation spectroscopy results showed that interaction between water molecular and DAAM structural unit weakened prior to that between water molecular and NVP structural unit due to rising temperature. The concentration dependence of the increasing specific viscosity indicated that the aggregation concentration (Cg) of the polymer solution decreased with increasing temperature.Dynamic light scattering experiments showed that the hydrodynamic size increases with increasing temperature above the LCST. The results comprehensively showed that the P(NVP- co -DAAM) copolymer exhibits a sensitive temperature response, and the P(NVP- co -DAAM) structure has good biocompatibility, indicating its significant potential for application in biomedicine and related fields. Graphical