Analysis of hydration states of thermo-responsive poly(<i>N</i>-isopropylacrylamide) by the combination of infrared absorption spectroscopy and multivariate curve resolution

Abstract Water molecules in the vicinity of polymers influence the behaviors of solvated polymeric materials. However, understanding the behavior of these vicinal water molecules is challenging. Using a multivariate curve resolution approach, we present a method for extracting the infrared absorption spectra of vicinal water of poly(N-isopropylacrylamide) (PNIPAAm). Our analysis successfully quantified vicinal water molecules, showing significantly higher hydration numbers in the hydrophilic state, providing insights into the role of vicinal water in the temperature-dependent affinity switching of PNIPAAm toward cells.