Kinetics of the temperature-induced volume phase transition in poly(2-(2-methoxyethoxy)ethyl methacrylate) hydrogels of various topologies

Hydrogels based on thermo-responsive 2-(2-methoxyethoxy)ethyl methacrylate (pMEO2MA) are regarded as bioinert replacements of poly (N-isopropylacrylamide) in many biomedical applications. Here, we study kinetics of temperature-induced volume phase transitions (VPT) of pMEO2MA-based hydrogels of various network architecture during their water sorption and desorption processes by means of dielectric spectroscopy. Maxwell-Wagner-Sillars (MWS) polarization processes of two distinct origins develop in the course of VPT in the hydrogels. In the hydrogel with bare pMEO2MA network we observe MWS process resulted probably from interfacial polarization on microheterogeneities in the hydrogel and an additional MWS polarization linked to formation of the so-called dense skin-layer. In the hydrogel with its network grafted with dangling chains we observe only the microheterogeneities-related process; the process associated with formation of the skin-layer is not present, possibly due to more effective water diffusion out of the hydrogel. We determine relaxation times related to rearrangements of the polymer networks and to the diffusion of water during the hydrogel VPT in the both directions of the transition.