Polyurethane prepolymers with reduced functionality having terminal alkoxysilane and OH groups, a method of preparing them and their use

A process for preparing a polyurethane prepolymer having terminal alkoxysilane and OH groups which comprises reacting

• A) a polyurethane prepolymer prepared by incomplete reaction, of
• i) an aromatic, aliphatic or cycloaliphatic diisocyanate component having an NCO content of 20 to 60% by weight with
• ii) a polyol component comprising a polyoxyalkylene diol having a number average molecular weight of 3000 to 20,000,
• wherein the reaction is stopped after 50 to 90% of the OH groups of component ii) are reacted and 10 to 50% are unreacted, with
• B) a compound having alkoxysilane and amino groups, of formula (I)
• 7
• wherein
• X, Y and Z are the same or different and represent linear or branched C1-C8 alkyl or C1-C8 alkoxy radicals, provided that at least one of the radicals represents a C1-C8 alkoxy group,
• R represents a linear or branched alkylene radical with 1 to 8 carbon atoms,
• R′ represents hydrogen, a C1-C8 alkyl radical, a C6-C10 aryl radical or a radical of formula (II)
• 8
• wherein
• R″ and R′″ are the same or different and represent linear or branched alkyl radicals with 1 to 8 carbon atoms.