Poly(1,6-heptadiyne)-based polyacetylenes as a new class of pi-conjugated polymer were designed and prepared. In general, the Mo-based catalysts were found to be very effective for the cyclopolymerization of 1,6-heptadiyne and its derivatives with various substituents, whereas the W-based catalysts gave only a low yield of polymers for the same polymerization. The chemical structures of the resulting poly(1,6-heptadiyne)s were characterized by various instrumental methods such as NMR, IR, UV-visible spectroscopies and elemental analysis to have the conjugated polymer backbone systems with functional substituents. The microstructures of poly(1,6-heptadiyne) homologues were found to be dependant on the catalysts, the polymerization conditions, the size of substituents, etc. Poly(1,6-heptadiyne) derivatives having bulky substituents revealed excellent oxidative stability in air relative to polyacetylene and poly(1,6-heptadiyne). The examples of poly(1,6-heptadiyne)s having such peculiar functionalities as side-chain liquid crystalline, nonlinear optical, photoconductive, photorefractive, and self-dopable ionic groups were presented. (C) 2003 Elsevier B.V. All rights reserved.