Solutions of polyvinyl alkyl ketones or interpolymerization products from mixtures consisting of not less than 50 per cent by weight of vinyl alkyl ketones together with other polymerizable unsaturated compounds, are prepared by (a) dissolving the polymer or interpolymer in a mixture of water and a monohydric alcohol miscible with water, or (b) causing the monomeric substances to undergo polymerization, with the aid of heat and/or a polymerization catalyst, in a mixture of water and a monohydric alcohol miscible with water, the alcohol, in each case, being present in an amount of 30 to 80 per cent by weight of the mixture. The polymerization may be carried out continuously by introducing the reaction mixture into a tall tubular apparatus and continuously removing the product from the bottom of the apparatus. Specified alcohols are methyl, ethyl, and propyl alcohols and alcohols containing two or more hydroxyl groups of which only one is unsubstituted, e.g. glycol monoethers. Specified ketones are vinyl methyl and vinyl ethyl ketones, and the other polymerizable unsaturated compound may be acrylic acid, acrylic acid methyl-, ethyl-, or propyl-ester, acrylic acid nitrile, styrene, or vinyl ethyl-, propyl-, or butyl ether. In examples: (1) polyvinyl methyl ketone is dissolved in aqueous ethyl alcohol; (2) an aqueous suspension or emulsion of an interpolymer of vinyl methyl ketone and vinyl n-butyl ether is dissolved by the addition of aqueous ethyl alcohol; (3) vinyl methyl ketone is dissolved in aqueous ethyl alcohol containing hydrogen peroxide and polymerized by heat; the solution of polymer may be diluted with other solvents, e.g. acetone or glycol formal; (4) a mixture of vinyl methyl ketone and acrylic acid is dissolved in aqueous methyl alcohol containing hydrogen peroxide and polymerized by heat; and (5) a mixture of vinyl methyl ketone and acrylic acid methyl ester is dissolved in aqueous isopropyl alcohol containing hydrogen peroxide and polymerized by heat.