A variety of transition metal catalysts have been developed for the polymerizations of different types of substituted acetylenes. [Rh(nbd)Cl]₂ (nbd = 2,5-norbornadiene) and WCl₆-Ph₄Sn/dioxane are effective catalysts for polymerizations of acetylenes containing polar functional groups such as cyano, ether, and ester units. Stereoregular poly(phenylacetylenes) are produced by aqueous polymerizations catalyzed by Rh complexes including [Rh(nbd)Cl]₂, [Rh(cod)Cl]₂, Rh(cod)(pip)Cl, [Rh(cod)Cl]₂(pda), Rh(cod)(bbpmt), Rh(cod)(NH₃)Cl, [Rh(cod)(mid)₂]PF₆, Rh(nbd)(tos)(H₂O), and Rh(cod)(tos)(H₂O) (cod = 1,5-cyclooctadiene, pip = piperidine, pda = o-phenyldiamine, bbpmt = bis(4-t-butyl)-2-pyridylmethanethiolate, mid = N-methylimidazole, and tos = p-toluenesulfonate). Air-and moisture-stable metal carbonyl complexes W(CO)₃(mes) (mes = mesitylene) and Mo(CO)₄(nbd) effectively initiate polymerizations of phenylacetylene and 1-chloro-1-octyne without the use of cocatalyst and photoirradiation. A number of transition metal compounds including TaCl₅, NbCl₅, Mo(CO)₄(nbd), [W(CO)₃cp]₂ (cp = cyclopentadiene), PdCl₂-ClSiMe₃, and Pd/C-ClSiMe₃ catalyze polycyclotrimerizations of terminal and internal diacetylenes (diynes) such as 1,8-nonadiyne, 1,9-decadiyne, 3,9-dodecadiyne, and 1,9-bis(trimethylsilyl)-1,8-nonadiyne, yielding soluble hyperbranched poly(phenylenealkenes) under mild conditions.