Solid-state copolymerization of 8,8-(1,4-phenylene)bis(5,7-octadiynyl N-(butoxycarbonylmethyl)carbamate) 1, a 1,4-bis(butadiynyl)phenylene derivative, and its perfluorophenylene derivative 2 was examined. Their mixed crystals with different mixing ratios were prepared by the slow-evaporation method. When the molar mixing ratio of 2 with respect to the total monomers is 60% or more, the mixed crystals have uniform composition and the crystal structures were found to be similar to those of 2. The mixture of 1 and 2 in 3:7 ratio was able to polymerize in the solid state upon UV irradiation although 2 is polymerizable but 1 is not polymerizable in the solid state. The copolymer structure was considered to be the single-chain-type polydiacetylene.