We report the synthesis of various substituted polyacetylenes including a novel poly(dinaphthylacetylene), poly{2-(2-ethylhexyloxy)-6-[2-(6-methoxynaphthyl-2-yl)ethynyl]naphthalene}, by the use of a WCl6-Ph4Sn catalyst system, and systematically investigate their solution properties. It is found that poly(diarylacetylene)s such as poly(dinaphthylacetylene)s and poly(diphenylacetylene)s exhibit a solution morphology between rod-like and semi-flexible, whereas the less bulky poly(phenylacetylene)s, poly(silylacetylene)s, and poly(tert-butylacetylene) exhibit a random coil morphology.