Abstract: There is described a process for the production of an ethanol solution of an ethyl or butyl half-ester copolymer of maleic anhydride and a methyl vinyl ether which comprises: (a) copolymerizing the monomers in acetone as solvent by simultaneously feeding molten maleic anhydride, a molar excess of methyl vinyl ether, and a solution of a free radical initiator in acetone, into a reactor precharged with acetone, at about 68.degree.-85.degree. C., preferably 70.degree.-80.degree. C.; (b) esterifying the acetone solution of said copolymer with ethanol or butanol; and then (c) solvent exchanging ethanol for acetone by continuously injecting vapors of ethanol at about 85.degree.-95.degree. C. into said copolymer solution while simultaneously distilling out acetone therefrom at atmospheric pressure.