Polymerization and copolymerization of 2,4-dichlorophenylacetylene and 3-heptyne was carried out using tungsten-containing catalysts. The monomer reactivity ratios showed that the phenylacetylene was more reactive than 5-heptyne by a factor of 3.2. Relationships between the monomer composition, gas permeability and selectivity were investigated, and it was found that the incorporation of 2,4-dichlorophenylacetylene decreases the permeability, but increases selectivity for the gas mixtures tested in this work. The electrical conductivities of the polymers were also determined.