. "Particularly useful interpolymers of maleic anhydride, or its substituted derivatives, include those polymers represented by the following general formula: wherein R, R and R each represents a hydrogen atom or a lower alkyl group, such as methyl, ethyl, etc., R, represents a hydrogen atom, an alkyl group (e.g., methyl, ethyl, etc), a monocyclic aryl group (e.g., phenyl, tolyl, etc.) or a carbalkox" . . . .