4’-Ethynylbenzo-15-crown-5 (EB15C5) polymerized with high yields in the presence of (bicycle[2.2.1] hepta-2,5 -diene)rhodium(I) chloride dimer and triethylamine as a cocatalyst in chloroform at 30 degrees C. Common catalysts for the polymerization of substituted acetylenes, WCl6 and MoCl5, did not produce any polymer from EB15C5. The structure of the main chain for poly(4’-ethynylbenzo-15-crown-5) (PEB15C5) was determined to be predominantly cis form, based upon the relatively sharp signals attributed to the main chain atoms that was observed in the H-1 and C-13 NMR spectra. The cation-binding properties of PEB15C5 are very similar to that of poly(4’-vinylbenzo-15-crown-5), and the selectivity is in the order of K+ > Rb+ much greater than Cs+ Na+, Li+. The electrical conductivity of PEB15C5 increased from 1.3 X 10(-10) to 1.3 X 10(-6) S . cm(-1), when the polymer was doped with iodine.