A method of using substituted olefin polymers prepared by reacting one or more C2-C10 mono-olefin polymers having a number average molecular weight of about 300 to about 5,000 with C4-C10 monounsaturated dicarboxylic acid derivatives and compositions comprising the substituted olefin polymers for preventing fouling of hydrocarbon processing equipment, especially ethylene dichloride distillation units.