Copolymers of sodium 4-styrene sulphonate and vinyl derivatives of nitrogen-containing heterocycles

Abstract

The formation of ion-exchange composite materials based on high molecular weight precursors appears to be an intensively developing area in the synthesis of proton-conducting membranes for fuel cells. In such membranes, proton transfer is often provided by functional polymers simultaneously containing sulphonic acid groups in their composition units along with fragments of vinyl derivatives of nitrogen-containing heterocyclic bases. Proton exchange activity in the latter is determined by the possibility of doping with inorganic acids. In the framework of this study, for the further formation of hybrid composite membranes under conditions of radical initiation, copolymers of sodium 4-styrene sulphonate (SSt) with 4-vinylpyridine (VP) and 1-vinylimidazole (VIM) were obtained. The monomodal nature of the turbidimetric titration curves for solutions of copolymerisation reaction products indicates the presence of true copolymers during the process of formation. The composition and structure of the copolymers were characterised using data from elemental analysis, as well as from IR and 13 C NMR spectroscopy. Constants of the relative activity for the monomers and the microstructure parameters of the polymer chains are calculated according to the non-linear leastsquares method using the MathCAD package. The calculated copolymerisation constant values indicate a greater reactivity of SSt in comparison with nitrogen-containing monomers. The lengths of the monomer unit blocks depend on the composition of the initial mixture and vary over a wide range from 1 to 18. The possibility of varying the length of the unit blocks in the composition of the copolymers will affect the ion-conducting properties of hybrid composites formed on their basis. The stability of the copolymers to thermal oxidative degradation by heating in air was studied using the differential scanning calorimetry (DSC) method. The copolymers demonstrated significant thermo-oxidative stability. Decomposition temperatures were 350 °С and 400 °С for SSt-VIM and SSt-VP copolymers, respectively.