Preparation of amphoteric latex by modification of styrene–acrylamide copolymer latex

Styrene–acrylamide copolymer latex prepared from the polymerization in an emulsifier‐free aqueous medium was treated with hypochlorite and sodium hydroxide. The resulting latex indicated amphoteric property due to amino and carboxyl groups formed by the Hofmann reaction and competitive hydrolysis of amide groups, respectively. Amphoteric latices with the same particle size but different charge density (1.0–3.0 ionic groups/100 Å2) and different isoelectric points (6.4–9.2) have been prepared by changing the reaction conditions.