Reason for the High Solubility of Chemically Modified Poly(vinyl alcohol)s in Aqueous Solution

Abstract

Partially chemically modified poly(vinyl alcohol) synthesized via random introduction of a diol-type monomer (mPVA) shows much higher solubility in water than normal homo poly(vinyl alcohol) (PVA). To clarify the reason for the high solubility of mPVA, we investigated the temperature dependencies of the hydration numbers per hydroxy group (mOH) for mPVA at various diol-type monomer contents from x = 0 (PVA) to 0.12 using extremely high frequency dielectric relaxation measurements up to 50 GHz over a temperature range from 10 to 70 °C. The values of mOH for mPVA in the temperature range below 20 °C looked constant and increased from 2.4 to 3.4 with increasing x. Above 20 °C, the values of mOH decreased with increasing temperature and approached a constant value close to unity above 70 °C irrespective of x. Although the random introduction of the diol-type monomer into the mPVA backbones effectively increased the mOH values, broad dehydration was commonly observed at approximately 40 °C irrespective of the x value. It is likely that the presence of the diol-type monomers in the polymer backbone considerably disturbs the highly developed sequential intramolecular hydrogen bonding between adjacent hydroxy groups in the normal homo PVA.