Transparent, compact polyurethane casting compositions that are sterilizable with superheated steam, process for preparing same, and their use, particularly for medical-technical articles

A transparent, substantially compact polyurethane casting composition which is sterilizable with superheated steam, wherein the composition is produced by a method comprising the steps of:

• A. preparing a modified diphenylmethane diisocyanate wherein liquid at 23.degree. C., the modified diphenylmethane diisocyanate being prepared by a process of reacting a diphenylmethane diisocyanate isomer mixture with at least one polyoxypropylene polyol wherein the diphenylmethane diisocyanate isomer mixture comprises from about 60 to about 90 weight percent of 4,4'diphenylmethane diisocyanate, from about 40 to about 8 weight percent of 2,4' diphenylmethane diisocyanate, and from 0 to 5 weight percent of 2,2'-diphenylmethane diisocyanate, and wherein the polyoxypropylene polyol has a molecular weight of from about 350 to about 800, the polyoxypropylene polyol having been produced by using at least one initiator selected from the group consisting of glycerine and trimethylol propane, and wherein the reaction of the diphenylmethane diisocyanate isomer mixture with the polyoxypropylene polyol is carried out with a ratio of NCO:OH of from about 2.5:1 to about 15:1, whereby the modified diphenylmethane diisocyanate is produced, and
• B. reacting the modified diphenylmethane diisocyanate with at least one compound having at least two reactive hydrogen atoms thereon.