Recrystallizable Water Classified as Intermediate Water in Acrylate Polymer Matrices: Governed by Polymer Chain Dynamics, Not by Water Structure

The recrystallization behavior of water and the static water structures in nonwater-soluble acrylate polymers were investigated using differential scanning calorimetry (DSC) and mid-infrared (mid-IR) spectroscopy. This study explores the relationship between the glass transition temperature (<i>T</i>_g) of hydrated polymers, the recrystallization temperature of water (<i>T</i>_RC), and the static water structures sorbed into the polymers. The results indicate that it is difficult to infer the presence of recrystallizable water in polymers solely from the static water structure at room temperature, as revealed by the OH stretching region in the mid-IR spectrum. Similarly, predicting the <i>T</i>_RC based on the static water structure is not straightforward. In contrast, a strong correlation was observed between the <i>T</i>_RC and the <i>T</i>_g of the hydrated polymers. These findings clearly demonstrate that water recrystallization in polymers is not governed by the static water structure at room temperature but rather by the polymer dynamics associated with the glass transition behavior of hydrated polymers.