slowly reduced to 20 torr and that pressure was maintained for 15 minutes the system was then brought to atmospheric pressure with nitrogen and the hot prepolymer drained into glass jars and sealed the hydroxyl equivalent weight was determined by the phenyl isocyanate titration method using diglyme as the solvent the hydroxyl equivalent weight of this example was 1 000 and can range from 750 to 1500 in a 1 000 ml three necked round bottomed flask equipped with a stainless steel stirrer inert gas inlet and a reflux condenser were charged 200 grams 0 10 moles of the sulfonated prepolymer from example 9 the prepolymer was dissolved in 200 grams of dry methyl isobutyl ketone with stirring at 100 u00b0 c the solution was cooled to 60 u00b0 c and 87 0 grams 0 50 moles of tolylene 2 4 diisocyanate was charged in one portion the reaction mixture was stirred at 80 u00b0 c for 30 minutes after which 85 2 grams 0 2 moles of diol 2 1 cyclohexane dimethanol maleic anhydride condensation product were charged the reaction was stirred for an additional 30 minutes at 80 u00b0 c after which 12 4 grams 0 20 moles of ethylene glycol was charged the reaction temperature was raised to 115 u00b0 c and stirring was continued for 2 to 3 hours or until the high viscosity of the reaction prevents stirring the reaction was quenched by the slow addition of 300 grams of 2 methoxyethanol and the finished polymer was stored in solution the sulfonate equivalent weight of.