Terpolymers of maleic anhydride and their use as scale control agents

A polymeric agent comprising a terpolymer, its hydrolyzed form, and the alkali metal, amine and ammonium salts thereof, said terpolymer consisting essentially of 30 to 55 mole percent maleic anhydride, 30 to 65 mole percent acrylamide or methacrylamide and 5 to 15 mole percent third monomer selected from the group consisting of styrene, .alpha.-methyl styrene, alkyl acrylate or alkyl methacrylate having from one to eight carbon atoms in the alkyl group and 1-alkene having from four to ten carbon atoms, said terpolymer being characterized by a relative viscosity of about 1.02 to 1.10 in dimethyl sulfoxide at a concentration of 0.5 g. per deciliter, and by solubility of less than 0.10 g. per g. of solution (water) at ambient temperature.