Polydiphenylsiloxane-polydimethylsiloxane-polydiphenylsiloxane triblock copolymers were prepared by two methods. The first approach was the sequential addition of the monomers. The anionic polymerization of hexamethylcyclotrisiloxane initiated by dilithio diphenylsilanolate gave alpha,omega-bis(lithio dimethylsilanolate)polydimethylsiloxane, which was added to hexaphenylcyclotrisiloxane at similar to 120 degrees C to yield the desired triblock material. In the other, a convergent approach was used. Excess alpha-vinyldimethylsiloxypolydiphenylsiloxane was coupled to alpha,omega-bis(hydrido)polydimethylsiloxane by a Pt-catalyzed hydrosilylation reaction to give the triblock material. The formation of distinct blocks with regular microstructures in these materials was confirmed by H-1, C-13, and Si-29 NMR spectroscopy as well as differential scanning calorimetry. The molecular weights were determined by gel permeation chromatography, and the thermal stabilities were evaluated by thermogravimetric analysis. Dynamic mechanical analysis was used to confirm thermal transitions obtained by differential scanning calorimetry and to evaluate the mechanical properties of the materials. (c) 2006 Wiley Periodicals, Inc.