of unreacted tdi similarly the cure time and temperature may also be varied by those skilled in the art to allow longer or shorter processing times and fine tuning of ultimate properties when desired post cure heat conditioning may also be employed at the option of the skilled artisan the following examples further illustrate the best mode contemplated by the inventor for the practice of his invention a poly tetramethylene glycol of about 1 000 molecular weight and a poly oxypropylene glycol of about 1 000 molecular weight the mixture then having equivalent weight of 500 is chain extended to about 6 00 nco content at an nco oh ratio of about 1 9 to hylene tm 3 6 equivalents is added a mixture of poly tetramethylene glycol 1 488 equivalents and poly oxypropylene glycol 0 372 equivalents is added slowly such that the temperature is kept below 55 u00b0 c after addition is complete the reaction is heated under an inert atmosphere at 80 u00b0 c for two hours the reaction product is then passed through a wiped film molecular still at a jacket temperature of 150 u00b0 c at a pressure of 0 5 0 8 mm hg to obtain a low unreacted tdi prepolymer s g 1 074 25 u00b0 c a polyoxy tetramethylene glycol 2 000 molecular weight poly oxypropylene glycol 2 000 molecular weight 80 20 blend is endcapped with tdi to 4 45 nco at an nco oh ratio of 2.