9-Ethynylanthracene has been polymerized at 80°C by use of complex phosphinic, arsinic, and stibinic initiators, e. g., NiCl2′2PPh3, and the obtained products have been divided into benzene-soluble and benzene-insoluble fractions. It has been shown that the benzene-insoluble polymer has a conjugated polyenic structure while the soluble polymer, withMless than 1500 daltons, contains dihydroanthracene units in the backbone in addition to the conjugated double bonds. It has been found that by using the above initiators the polymers are mainly cis. The cis to trans isomerization has been shown by DTA and DSC measurements to occur between 260 and 290° C.