A method of emulsifying a substituted cyclic dicarboxylic acid anhydride sizing agent such as alkenyl succinic anhydride (ASA), primarily for papermaking operations, uses a cationic reaction polymer synthesized from an epihalohydrin and a polyamine, preferably a polyalkyleneamine. The synthesis of the reaction product is controlled to obtain a polymer end product viscosity, by Brookfield, ranging between 50 and 300 cps at 25.degree. C. and at 30 to 35% solids. Alternatively, the preferred cationic polymers can be described as having an intrinsic viscosity value in a 0.2M NaCl solution of 0.18 to 0.35 dL/gm at 30.degree. C. The polyamine-epihalohydrin polymers can also be optionally used in combination with a surfactant for further emulsifying of the ASA size.