PURPOSE: To obtain the titled water-soluble polyvinyl alcohol (PVA) having improved viscosity stability of an aqueous solution thereof, by saponifying a copolymer consisting of a vinyl ester and two olefinically unsaturated monomers containing respective specific groups.
CONSTITUTION: A copolymer obtained by copolymerizing (A) a vinyl ester, preferably vinyl acetate, with (B) an olefinically unsaturated monomer, e.g. vinyltrimethoxysilane, containing silyl groups and (C) an olefinically unsaturated monomer, e.g. N-(1,1-dimethyl-3-dimethylaminopropyl)acrylamide, containig ionic hydrophilic groups in the presence of (D) a radical initiator is saponified to give the aimed polyvinyl alcohol (PVA). The above-mentioned copolymerization is preferably carried out in the form of solution polymerization in the presence of a lower alcohol. Furthermore, the saponification is preferably carried out by using a solution of the copolymer in an alcohol in the presence of NaOH catalyst.
TANAKA TAKU
OKAYA TAKUJI
