The tentative identification of the reactive species in the condensation of Cp2TiCl2with salts of diacids to form titanium polysters is made. The reactive species are believed to be the same for both aqueous solution and interfacial systems, i.e., R -CO2−and Cp2Ti2+with reaction occurring in the aqueous phase. The condensation of Cp2TiCl2with disodium terephthalate in interfacial systems occurs via a pseudo-first-order reaction: