In making the copolymers there may be used such materials as methyl or ethyl acrylates; methyl, ethyl isobuty-l, and methoxyethyl methacrylates; methacrylamide and N-methylacrylamide: acrylonitrile and methacrylonitrile; styrene, vinyl naphthalene, and the like or mixtures of two or more of these compounds.