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Poly(styrene-b-vinylphosphonic acid) diblock copolymers have been prepared via sequential anionic polymerization and evaluated as nanostructured polymer electrolytes. The ionic block copolymers were synthesized by first initiating the polymerization of styrene using n-butyllithium in tetrahydrofuran at -78 °C. 1,1-Diphenylethylene was then added to the living polystyryl anions before charging diethyl vinylphosphonate to polymerize the second block. The poly(diethyl phosphonate) block was subsequently completely hydrolyzed to obtain the poly(vinylphosphonic acid) block. Analysis by calorimetry showed two distinct glass transitions of the acidic copolymers, indicating phase separation between the two blocks. The glass transition temperature of the densely phosphonated blocks was strongly influenced by the formation of anhydride links through reversible self-condensation reactions at elevated temperatures. Studies of thin copolymer films by tapping mode atomic force microscopy revealed nanophase-separated morphologies with continuous phosphonated domains. In addition, the acidic block copolymers were found to self-assemble into spherical micellar nanoparticles which, in turn, formed branched arrays of supramolecular "necklace-like" chain structures. Block copolymers equilibrated at 25 °C and 98% relative humidity reached proton conductivities in the order of 30 mS/cm at 130 °C.

The thermal stability of styrene grafted and sulfonated poly(vinylidene fluoride), PVDF-g-PSSA, proton conducting membranes has been studied using thermal gravimetric analysis in combination with mass spectrometry and thermochromatography. The matrix polymer, PVDF, and the non-sulfonated counterpart, PVDF-g-PS, were studied as reference materials. It was found that the degradation of the PVDF-g-PS membrane proceeds in two steps starting at ca. 340 °C with the evolution of degradation products typical of polystyrene. The PVDF-g-PSSA membranes are stable to around 270 °C even in a strongly oxidising atmosphere. The degradation starts with the simultaneous evolution of water and sulfur dioxide. The polystyrene grafts start decomposing at 340 oC in the PVDF-g-PSSA membranes. Thus the membranes are suitable for tests in electrochemical applications at elevated temperatures.