Selective polyurethane prepolymer synthesis

Process for the production of polyurethane prepolymers with a molecular weight profile, measured by gel permeation chromatography, of the polyurethane prepolymers from 2000 Da (x1) to 200000 Da (x3) along an x-axis has a first section with an area integral FI and a second section with an area integral FII, for which a ratio FII/FI is between 0 up to and including 0.4, where the first section extends from x1 to x2 and the second section extends from x2 to x3, and x2 defines an extreme point between the last intensity maximum (M1a) in the first section, situated in the region of the molecular weight of the hydroxy-functionalized polymer, and a subsequent intensity maximum (M2) in the second section, by a reaction of

• I. isophorone diisocyanate (IPDI) with
• II. a hydroxy-functionalized polymer having a number-average molecular weight Mn of 3500 to 100000 Da,
• in the presence of a catalyst, characterized in that,
• the molar ratio of NCO groups to hydroxyl groups in the reaction of I. with II. is from 3.0:1 to 1.8:1 and that the temperature in the reaction of I. with II. is between 20° C. and 90° C. and wherein the catalyst is heptaisobutyl POSS-titanium (IV) ethoxide (TiPOSS) and the total catalyst amount is between 3 and 80 ppm, based on the total weight of the hydroxy-functionalized polymer used.