Process for preparing a mixed silane-terminated polymer by reacting a polyol component A) with a diisocyanate component B) comprising 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate), with at least one isocyanatosilane C) and with an aminosilane E), in which the urethanization reaction is carried out in the presence of at least one catalyst D) which is free of organically bonded tin, wherein the process is conducted so that first, some of the hydroxyl groups of the polyol component A) are reacted with the diisocyanate component B) and, after reaching a desired NCO content, preferably when at least 40% of the NCO groups have reacted, in a second step the aminosilane is added in such an amount that, and reacted with the free NCO groups of the OH- and NCO-functional prepolymer obtained in the first step until, no free NCO groups are detectable in the reaction mixture any longer, and the still-free hydroxyl groups of the reaction product are then finally reacted with the isocyanatosilane C), characterized in that the catalyst D) is selected from a group of compounds comprising: - an organometallic compound of magnesium, zinc, gallium, scandium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, yttrium or lutetium, an organometallic compound being understood to be a compound which has at least one ligand bonded to the abovementioned metals (Me) via an oxygen atom, and the ligands being selected from the group consisting of alkoxy group, sulfonate group, carboxylate group, dialkylphosphate group, dialkylpyrophosphate group and β-diketonate group, where all ligands may be identical or different from each other, - or mixtures of the abovementioned compounds. wherein the process is conducted so that first, some of the hydroxyl groups of the polyol component A) are reacted with the diisocyanate component B) and, after reaching a desired NCO content, preferably when at least 40% of the NCO groups have reacted, in a second step the aminosilane is added in such an amount that, and reacted with the free NCO groups of the OH- and NCO-functional prepolymer obtained in the first step until, no free NCO groups are detectable in the reaction mixture any longer, and the still-free hydroxyl groups of the reaction product are then finally reacted with the isocyanatosilane C), characterized in that the catalyst D) is selected from a group of compounds comprising: - an organometallic compound of magnesium, zinc, gallium, scandium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, yttrium or lutetium, an organometallic compound being understood to be a compound which has at least one ligand bonded to the abovementioned metals (Me) via an oxygen atom, and the ligands being selected from the group consisting of alkoxy group, sulfonate group, carboxylate group, dialkylphosphate group, dialkylpyrophosphate group and β-diketonate group, where all ligands may be identical or different from each other, - or mixtures of the abovementioned compounds. - an organometallic compound of magnesium, zinc, gallium, scandium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, yttrium or lutetium, an organometallic compound being understood to be a compound which has at least one ligand bonded to the abovementioned metals (Me) via an oxygen atom, and the ligands being selected from the group consisting of alkoxy group, sulfonate group, carboxylate group, dialkylphosphate group, dialkylpyrophosphate group and β-diketonate group, where all ligands may be identical or different from each other, - or mixtures of the abovementioned compounds.