9,9-Bis(2'-ethylhexyl)-2,7-diethynylfluorene (1) or 1-(2'-ethylhexyloxy)-2,5-diethynyl-4-methoxybenzene (2) react in the presence of the [{RuCI(mu-Cl)(p-cymene)}](2)/AcOH catalytic system to yield the corresponding poly(aryleneethynylenevinylene) pi-conjugated homopolymers, featuring the areneenyne repeat unit (Ar-C C-CH=CH-) and characterized by high regio- and stereoselectivity [(E) > 93 %]. The copolymerization of 1 and 2 affords poly-(E)-FL-ethynylenevinylene-co-(E)-MEH-ethynylenevinylene [FL = fluorene; MEH = 1-(2'-ethylhexyloxy)-4-methoxybenzene], as the first example of a random copolymer derived from the polyaddition process of aromatic diynes. The catalytic system of this atom-economic polyaddition process is formed in situ from the commercially available ruthenium dimer and acetic acid and promotes the C-C coupling at room temperature. The branched 2-ethylhexyl chains in the arene moiety assist the formation of polymers with degrees of polymerization in the range of 9-20 repeat units. The optical properties of the new polymers were studied in chloroform solution and in film and compared to those of the main classes poly(arylenevinylene) and poly(aryleneethynylene) conjugated polymers. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)