The cyclopolymerization of 4,4-bis(hydroxymethyl)-1,6-heptadiyne (M1), 4-(carboxyethyl)-1,6-heptadiyne (M2), 4-(hydroxymethyl)-1,6-heptadiyne (M3), and 4-carboxy-1,6-heptadiyne (M4) using five different well-efined metathesis initiators was investigated. Control of molar mass was achieved with catalysts bearing trifluoro-acetate ligands. (CNMR)-C-13 experiments showed that poly-M2, prepared by the action of any catalyst consisted solely of five-membered ring structures, i.e., 1,2-(cyclopent-1-enylene) vinylene units. Effective conjugation lengths of all polymers were calculated from the corresponding UV-Vis absorption maxima, which varied reversibly with temperature.