Influence of poly(ethylene oxide) grafts on kinetics of LCST behavior in aqueous poly(N-vinylcaprolactam) solutions and networks studied by modulated temperature DSC

The (specific) heat capacity signal from modulated temperature DSC can be used to measure the onset of phase separation in aqueous poly(N-vinylcaprolactam) (PVCL) solutions, showing a type I LCST demixing behavior. Quasi-isothermal measurements through the phase transition show large excess contributions in the (apparent specific) heat capacity, caused by demixing and remixing heat effects on the time scale of the modulation. These excess contributions and their time-dependent evolution are useful to describe the kinetics of phase separation and to follow the related morphology development. Partial vitrification of the polymer-rich phase and a higher polymer concentration in the solutions lower the rate of phase separation. The introduction of hydrophilic poly(ethylene oxide) grafts onto PVCL lowers the demixing temperatures and markedly enhances the rate of phase separation, for both aqueous PVCL solutions and PVCL hydrogels.