The invention relates to reactive, urea-bonded alkoxysilanes based on polyether block copolymers reacted with diisocyanate, said copolymers being of the structure B-An in which the central block B consists of polyoxytetramethylene, polyoxyethylene, polybutadiene, polyisoprene, polyacrylate, polymethacrylate, polyamide, polyurethane or polyester units and the blocks A consist of polyoxypropylene units, and to a method for producing such alkoxysilanes. Preparations containing one or more urea-bonded alkoxysilanes can be used as an adhesive, sealant or coating agent.