Process for preparing alternating copolymers of olefinically unsaturated sulfonate salts and unsaturated dicarboxylic acid anhydrides

A copolymerization process which comprises reacting at a temperature of from about 50.degree. C. to 125.degree. C. in the absence of water approximately equimolar amounts of

• (a) an .alpha., .beta.-unsaturated dicarboxylic acid anhydride having the general structure:
• ##STR15## wherein R.sub.4 and R.sub.5 are the same or different and are independently selected from the group consisting of hydrogen, aryl, and C.sub.1 -C.sub.6 alkyl;
• and
• (b) an olefinically unsaturated sulfonate salt having the general structure:
• ##STR16## wherein R.sub.1, R.sub.2, and R.sub.3, are the same or different and are independently selected from the group consisting of hydrogen, aryl and C.sub.1 -C.sub.6 alkyl, x is 0, 1, or 2, and M is an alkali metal, alkaline earth, or ammonium;
• dissolved in an non-reactive polar organic solvent selected from acetic acid and dimethyl formamide in the presence of an effective amount of an azo initiator to form a substantially alternating copolymer containing approximately equimolar amounts of .alpha., .beta.-unsaturated dicarboxylic anhydride recurring polymerized units and olefinically unsaturated sulfonate salt recurring polymerized units and having a peak molecular weight of from about 1500 to 6000.