Synthesis, Microstructure And Performance Of Sulfonated SEBS For Proton Exchange Membranes

The work in this thesis was focused in obtaining a kind of proton exchange membrane with unique microstructure and low price. A novel hydrocarbon block copolymer membranes, sulfonated styrene/ethylene-butylenes/styrene triblock copolymer (S-SEBS) membrane, was prepared by the method of premix and solution casting. The synthesis process was studied and optimized, and the microstructures of products were characterized by FT-IR, DSC and AFM etc. The relationship between performance and microstructure was investigated in detail. Its microstructure model was discussed as well.The results showed that polystyrene block is sulfonated para to the alkyl moiety when the sulfonation degree of products was not very high, however, sulfonic acid groups would substitute ortho positions besides para positions with the further increase of the sulfonation degree. The sulfonation reaction efficiency would reach a peak when the mole rate of acetic anhydride and concentrated sulfuric acid was 1.5. The sulfonation degree of products would be higher as the volume rate of 1,2-dichloroethane and cyclohexane was 8. And when the temperature of sulfonation reaction was 50℃, the sulfonation degree of products would be higher. Moreover, It was found that the S-SEBS resin would only be swelling or partly soluble in the single polar solvent But it would be soluble and have a better membrane-forming property in the mixture solvent When heat treatment temperature rose, membrane would become brown and the selling rate would decrease. The point of 55℃ would be the better heat treatment temperature.The thermal decomposition temperature of sulfonic acid groups of S-SEBS membrane was 130℃, but the thermal stabilization of those who experienced high temperature heat treatment would decrease a little. The swelling rate of S-SEBS would increase with the sulfonation degree, and when sulfonation degree was over 50 percent, the membrane would be almost soluble in water. Conductivity, water uptake, and hydration coefficient all increased drastically at the point of 15 percent sulfonation degree, which exhibited the percolation threshold, then the first two kept increasing with the sulfonation degree growing but gradually became slow, and hydration coefficient came to the peak when the sulfonation degree was about 20. AFM showed that sulfonated PS phases were the cylinder structure with 20~30nm and have confluent trend. And the microstructure model showed that S-SEBS had a ordered microstructure and would reach the percolation threshold with smaller water volume than those random ion polymers (Nation et al).