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 (WC, 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 WC (1.07 wt %) shows reversible redistribution among the same five components with no ice-like signatures. At WC = 3.30 wt %, an ice Ih-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 WC and the onset of the ice-present regime at high WC, consistent with mobility-controlled reorganization of sorbed water coupled to polymer dynamics. Fixed-basis regression separates ice Ih 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 Ih contribution below 273 K is more consistent with interfacial dissolution followed by redistribution into polymer-hydrated environments than with simple bulk-like melting.