Alkoxysilyl-terminated preopolymers prepared by reacting an alkoxysilane with a prepolymer prepared by reacting a di- or polyisocyanate with both a low molecular weight diol or polyol and a high molecular weight polyol, the respective polyol components present within a specific ratio range, and giving rise to an increased content of urethane groups, and an inhomogenous distribution thereof exhibit high tensile strength and elongation, even without the use of fillers.