Effect of interactions between poly(vinyl alcohol) and urea on the water solubility of poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) is an important water-soluble polymer. Its many applications (e.g., textile sizing, dispersants, and adhesives) greatly depend on its water solubility and particularly on its dissolution rate in water. In this study, urea, combined with methanol, was adopted to improve the water solubility of PVA. The structures, properties, and dissolving mechanism of the modified PVA were studied with Fourier transform infrared spectroscopy, NMR, laser light scattering, differential scanning calorimetry, and wide-angle X-ray diffraction. The results showed that through specific chemical reactions between PVA and urea in methanol, isocyanate and methyl carbamate groups were generated on the lateral chains of PVA. These large side groups could effectively expand PVA macromolecular chains and hence increase their intermolecular distance, weaken the intramolecular and intermolecular hydrogen bonds of PVA, change the aggregation structure of PVA, and decrease its lattice energy and crystallinity. In addition, the isocyanate groups on the PVA macromolecular chains strongly interacted with water. All these effects benefited the water solubility of PVA. Therefore, the dissolution rate of the modified PVA increased by 50% versus that of the neat PVA, and the quality of the modified PVA aqueous solution was improved quite a bit. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009