Multicomponent Mid-Infrared Analysis of Cold-Crystallizable (Intermediate) Water in Poly(2-Methoxyethyl Acrylate)

Multicomponent analysis of mid-infrared spectra was used to characterize cold-crystallizable (intermediate) water sorbed in poly(2-methoxyethyl acrylate) (PMEA) through a reproducible phenomenological decomposition of the broad O-H stretching band. At 298 K, the O-H stretching band (3750-3050 cm^-1) is reproducibly represented by five Voigt components. These components are treated as reproducible phenomenological subbands used to track spectral-weight redistribution, rather than as uniquely separable molecular species. Increasing water content (W_C, 0.16-4.94 wt %) raises the total band area approximately linearly and continuously transfers spectral weight from high-wavenumber, polymer-hydrated monomer-like components to low-wavenumber, water-water associated components without threshold-like switching. Upon thermal cycling, low W_C (1.07 wt %) shows reversible redistribution among the same five components with no ice-like signatures. At W_C = 3.30 wt %, an ice I_h-like contribution appears only on heating (215-265 5K). Notably, a crossover around ∼215 K marks both the onset of strongly suppressed redistribution at low W_C and the onset of the ice-present regime at high W_C, consistent with mobility-controlled reorganization of sorbed water coupled to polymer dynamics. Fixed-basis regression separates ice I_h and nonice contributions, revealing preferential depletion of associated water components at onset and progressive recruitment of monomer-like components during growth. The subsequent decrease of the ice I_h contribution below 273 K is more consistent with interfacial dissolution followed by redistribution into polymer-hydrated environments than with simple bulk-like melting.