New functional acetylene, 1-ethynyl-4-iodobenzene, (p-iodophenylacetylene) was prepared, characterized (i.r., n.m.r., u.v. and mass spectra) and transformed into high-molecular-weight polymers. Various WOCl4-based and MoCl5-based catalysts were used in the polymerization, the former leading to the red soluble and the latter to dark red insoluble poly(p-iodophenylacetylene) (PIPA), respectively. Both types of PIPA are non-crystalline and they differ in the configurational structure which, however, could not be assigned with certainty. A too high molecular weight and/or cross-linking is suggested as a reason of insolubility of PIPA prepared on Mo-based catalysts. The soluble PIPA was found to degrade autoxidatively in tetrahydrofuran solution at room temperature obeying the kinetic laws of polymer random degradation. The determined value of the rate constant of degradation, 2.6 x 10(-6) min(-1), is slightly higher than that found for unsubstituted poly(phenylacetylene) (PPA), under the same conditions. PIPA was found to possess a higher photoconductivity than PPA at low and moderate electric fields. The Onsager model offers an adequate explanation for the measured dependence of the photogeneration efficiency of the applied electric field assuming the Gaussian distribution of the radii of charge-transfer states.