Insight into Hydration Behavior of Poly(Hydroxypropyl Acrylate) Block Copolymer by Temperature-Dependent Infrared Spectroscopy

Dynamic light scattering (DLS), microscope, temperature-dependent infrared (IR) spectroscopy with perturbation correlation moving window (PCMW) were used to investigate the phase transition of a thermo-sensitive copolymer poly(N,N-dimethylacrylamide)-b-poly(hydroxypropyl acrylate)-b-poly(N,N-dimethylacrylamide) (PDMAA-b-PHPA-b-PDMAA). The copolymer was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. In the DLS analysis, the sudden increase in particle size at 49 ℃ and the polymer droplets appearing at 49 ℃ in the microscope photos indicate that the lower critical solution temperature (LCST) of the copolymer is around 49 ℃. IR spectra show that the OH groups of PHPA change from hydration states to free ones. The redshift of the spectra in C-H bands indicates the dehydration of CH groups. The hydration C = O bands transform into free states or the other part, which owns stronger intermolecular interactions. Moreover, the O-H bands show a more responsive to temperature during the phase transition by PCMW analysis. The reduced hydrophilicity of O-H bands is not enough to stabilize the polymer in water, which leads to a phase transition.