To a three-liter, four-necked flask equipped with a one-liter addition funnel, thermometer, stirrer and reflux condenser is added 610 grams toluene. The contents are heated to reflux and maintained under a nitrogen blanket while a monomer mix of 112.5 grams maleic anhydride, 262.5 grams methyl methacrylate, 240 grams butyl acrylate, 135 grams styrene and 28.0 grams benzoyl peroxide are fed at a uniform rate over a three-hour period to the refluxing toluene. The contents are held for 15 minutes, a sample is taken, and a chaser catalyst of 140 grams toluene a 3.75 grams benzoyl peroxide is added over 30 minutes. Reflux is maintained for an additional 30 minutes, the flask is then equipped with a Dean-Stark trap and 20.6 grams of toluene-water removed after a 45-minute reflux. The final product has a solids content of 51.7% (104.2% conversion); a viscosity of 890 cps; anhydride 0.698 meq/g. and anhydride plus acid (using tetra-n-butyl ammonium hydroxide) 0.705 meq/g.; Mn 4,000; Mw 14,500.
