Dynamics of Intermediate Water in Biocompatible Poly(2-methoxyethyl acrylate) Revealed by Quasi-Elastic Neutron Scattering

Biocompatible polymers play a critical role in biomedical devices. A prominent example is poly(2-methoxyethyl acrylate) (PMEA), the biocompatibility of which is attributed to the presence of "intermediate water", which exhibits physical properties distinct from bulk water. Although various methods have investigated intermediate water features, the fundamental origin of its formation remains elusive. In this study, quasi-elastic neutron scattering was employed in combination with selective deuteration to independently investigate the dynamics of water molecules and PMEA chains. Our results resolved four modes of water motion: global diffusion, slow local diffusion, fast local diffusion, and molecular reorientation. This dynamics hierarchy aligns with the behaviors reported for poly(ethylene oxide); however, the PMEA hydration water molecules exhibit enhanced localization due to the microphase separation within the PMEA-water system.