A process for the production of an ethanol solution of an ethyl or butyl alkyl half-ester copolymer of maleic anhydride and an alkyl 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 68-85 °C, preferably 70-80 °C; (b) esterifying the acetone solution of said copolymer with ethanol or butanol; and (c) solvent exchanging ethanol for acetone by continuously injecting vapors of ethanol at about 85-95°C into said copolymer solution while simultaneously distilling out acetone therefrom at atmospheric pressure.