Gas transport and ionic transport in membranes based on polynorbornenes with functionalized imide side groups

This work reports the synthesis and hydrogenation of polynorbornenes with functionalized imide side groups, specifically, poly(N-phenyl-exo,endo-norbornene-5,6-dicarboximide), as well as the sulfonation of the hydrogenated polymer. The gas transport characteristics and permselectivity of membranes prepared from the three separated polymers were thoroughly investigated. The results show that hydrogenation of the starting polymer promotes packaging efficiency, which is even enhanced by further sulfonation of the hydrogenated chains. The economy of free volume is reflected in the permeation and permselectivity coefficients of membranes prepared from the polymers. The study of electromotive forces of concentration cells with the sulfonated membrane separating hydrochloric solutions of different concentration suggests that the membranes exhibit high permselectivity to protons that decreases as concentration increases. However, a sharp increase in the electromotive force occurs at high concentrations. The fact that this increase is not observed in the electromotive forces of concentration cells with sodium chloride in the compartment cells suggests the formation of pair ions between protonated imide groups and chloride ions at high concentration that restrains co-ions mobility in the membrane. The membranes exhibit pretty good permselectivity to protons and sodium ions which makes them useful for ionic separation applications, such as electrodialysis. However, owing to the low water uptake, the protonic conductivity of the membranes equilibrated with water is nearly 2 orders of magnitude below that reported for Nafion membranes.