A functional monomer containing the sodium sulfonate group, sodium 2-acrylamide-2-methylpropane sulfonate (SAMPS), the chemical formula being shown below, has been found useful for the production of modified poly(vinyl alcohol) containing the sodium sulfonate group, -SO3Na, in the molecular chain by solution copolymerization with vinyl acetate and alcoholysis. The poly(vinyl alcohol)s modified with a sodium sulfonate group show strong hydrophilic properties, which permits poly(vinyl alcohol)s of much lower degree of hydrolysis less than 80 mol% to dissolve in water. In contrast to the poly(vinyl alcohol) modified with carboxylic monomers, reported in the preceding paper, the solubility of the poly(vinyl alcohol) modified with a sodium sulfonate group is less sensitive to pH or to the presence of inorganic salts.[GRAPHICS]