The thermal and morphological behavior of the first complete homologous series of liquid-crystalline polyacetylene derivatives has been investigated by means of X-ray diffraction, differential scanning calorimetry, thermogravimetry, and polarizing optical microscopy. The influence of the spacer length on the thermal behavior and on the structure of the mesophases is discussed, All polymers except one form smectic monolayers at room temperature. For one spacer length, the formation of bilayers is observed. Despite the connection of the mesogens to the stiff, conjugated polymer main chain, most polymers exhibit highly ordered mesophases. Copolymerization of the mesogen-containing monomers with 1-octyne leads to a decrease of the supramolecular order with an increasing amount of comonomer in the polymer and finally to the formation of a new phase.