Polyurethanes from a three component prepolymer

Claim 1

A PROCESS FOR THE PREPARATION OF A POLYURETHANE WHICH COMPRISES PREPARING A PREPOLYMER BY REACTING AN ORGAINC POLYISCOYANATE WITH A MIXTURE CONTAINING A POLYHYDRIC ALCOHOL HAVING AT LEAST TWO AND NOT MORE THAN THREE HYDROXYL GROUPS AND AN ORGANIC COMPOUND HAVING A PLURALITY OF ALCOHOLIC HYDROXYL GROUPS, SAID ORGANIC COMPOUND HAVING A MOLECULAR WEIGHT ABOVE ABOUT 800 AND SELECTED FROM THE GROUP CONSISTING OF HYDROXYL POLYESTERS, POLYHYDRIC POLYALKYLENE ETHERS, POLYDRIC POLYTHIOETHERS AND POLYACETALS, SAID POLYHDRIC ALCOHOL HAVING A MOLECULAR WEIGHT BELOW ABOUT 500; THE AMOUNT OF SAID ORGANIC COMPOUND IS SUCH THAT AN EXCESS OF FROM ABOUT 300 TO ABOUT 900 PERCENT OF SAID POLYSIOCYANATE IS PRESENT WHEN CALCUALTED ON THE BASIS OF THE HYDROXYL GROUPS OF SAID ORGANIC COMPOUND AND IS SUCH THAT FROM ABOUT 150 TO ABOUT 300 PERCENT EXCESS OF SAID POLYISOCYANATE IS PRESENT AFTER REACTION WITH ALL THE HYDROXYL GROUPS OF SAID MIXTURE CONTAINING SAID POLYHDRIC ALCOHOL AND SAID ORGANIC COMPOUND AND SUBSEQUENTLY REACTING SAID PREPOLYMER WITH ADDITIONAL POLYHYDRIC ALCOHOL TO BRING ABOUT CROSSLINKING AND PRODUCE A HARD, ELASTIC NCO TERMINATED POLYURETHANE CASTING BY PLACING THE FINAL INTO A MOLD AND ALLOWING IT TO CURE.