High-resolution magic-angle-spinning NMR spectroscopy is used to investigate the phase transition of poly(N-isopropylacrylamide-co-acrylic acid) hydrogels crosslinked with N,N'-methylene bisacrylamide, hereafter poly(NIPAAm-co-AAc). Van't Hoff Delta H and Delta S for polymer dehydration are derived from temperature-dependent NMR spectra, and the thermodynamic data strongly support a four-stage dehydration mechanism for pure poly(NIPAAm). Acrylic acid stabilizes the hydration sphere around the polymer chains. Reduced amounts of water released during the phase transition translates into smaller values for Delta H and Delta S. Enhanced rehydration kinetics for poly(NIPAAm-co-AAc) is attributed to water remaining in the samples at elevated temperatures, which may produce facile diffusion pathways and enable faster rehydration kinetics than poly(NIPAAm).