Poly(arylene ether sulfone) has been successfully modified by a process of bromination followed by displacement of bromine with substituted acetylenes using a palladium catalyst. The degree of bromination and alkynylation, determined by H-1-NMR, was in the range of 98-50% and 92-45%, respectively. FT-IR and C-13-NMR confirmed the structure of the polymers. The final aim was to obtain a new material employable as a membrane for gas separation. Permeation properties of substituted poly(arylene ether sulfone) to carbon dioxide, methane, oxygen, and nitrogen were evaluated. Asymmetric membranes of alkynylated polymer were prepared by phase inversion technique.