the reaction time of course is dependent on the initial concentration of the starting materials and the temperature the preferred time is from 0 01 to 4500 hours more preferred 0 05 to 350 hours and most preferred from 0 06 to 200 hours to a stirred sluury of 82 4 kocn 1 02 mole in 2000 ml of dimethylformamide dmf at 75 u00b0 c 183g of tolylene diisocyanate 1 05 mole is added at a rate of 0 85 ml min by means of a syringe pump the entire operation is carried out in a nitrogen atmosphere following the addition the reaction mixture is stirred an additional 10 minutes the temperature lowered to 60 u00b0 c dry methanol added large excess and allowed to react for an additional hour to insure complete quenching the major product is insoluble in dmf and thus readily separated by a single filtration a trace dmf soluble product is obtained after solvent stripping the filtrate after vacuum drying at 80 u00b0 c to remove residual dmf and methanol the following yield and analytical data are obtained __________________________________________________________________________ aryl end group sup 2 average mol product yield sup 1 ratio 2m n 1 m 2 wt minimum __________________________________________________________________________dmf insoluble.