Five well-defined polymeric silane coupling agents, triethoxysilyl-terminated polystyrene (TESi-PS), substituted with polystyrene moieties of various molecular weights, were condensed in tetrahydrofuran, in the presence of methanesulfonic acid as the catalyst. The effects on the reaction rate of the molecular weight of TESi-PS, of the amount of included polystyrene, and of nonpolar solvents have been examined. The kinetic data provide ample evidence that the formation of aggregates, during the condensation reaction, accelerates the reaction rate. To explain the acceleration effect, an aggregational model is presented in which the ethoxysilyl groups are concentrated in the polar core. This model may be applied to other polymerization processes.