Mercaptosilanes are disclosed of the formula I wherein R1 is an alkyl polyether group —O—(R5—O)m—R6. They are prepared by a procedure in which a silane of the formula II is subjected to a catalyzed reaction with an alkyl polyether R1—H, R7—OH being split off, the molar ratio of the alkyl polyethers R1—H to the silane of the formula II is at least 0.5 and R7—OH is separated off from the reaction mixture continuously or discontinuously. They can be used in shaped articles.