PURPOSE: To obtain a water-soluble composite material having a thickening effect and forming a flexible tough film, by polymerizing a phosphate ester compound having an α,β-unsaturated group in an aqueous PVA solution and acetalizing the product.
CONSTITUTION: Polyvinyl alcohol is dissolved in water and, after purging the atmosphere in the reaction system with nitrogen, a polymerization catalyst is added to the reaction system. 1W50wt% phosphate compound, based on the polyvinyl alcohol, is added to the reaction system and polymerized by heating to 40W100°C. When the amount of the phosphate compound added is outside the above range, the objective can not be attained. After completion of the polymerization, the product is acetalized by adding, preferably, 1W30wt%, based on the polyvinyl alcohol, aldehyde compound at 10W80°C in the presence of an acid catalyst. After the reaction, the reaction mixture is neutralized to a pH of 6W9 by the addition of caustic alkali, ammonia, an organic amine, or the like and then used at this pH.
WATANABE HIROSHI
KATOU HIROKAZU
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