Polyacetylene (I) was prepd. by ring-opening metathesis polymn. of benzvalene in the presence of non-Lewis acidic W alkylidene catalysts to give polybenzvalene, followed by isomerization in the presence of HgCl2. I had low crystallinity and elec. cond. 1 s/cm upon doping with iodine. [on SciFinder(R)]