Poly(p-methoxyphenylacetylene) was obtained by the reaction of p-methoxyphenylacetylene (MOPA) with the vanadium acetylacetonate-aluminum triethyl V(acac)(3)-AlEt3 homogeneous catalyst system. The crude product was always a mixture of 1,2,4- and 1,3,5-tris(p-methoxyphenyl)benzene and poly(MOPA) of low averaged molecular weight. The 1,2,4- and 1,3,5-cyclotrimers versus poly(MOPA) ratio was analyzed. The poly(MOPA) obtained under different conditions, on the basis of the spectroscopic data, always shows a cis-transoidal stereo-regular structure. Molecular mass of poly(MOPA) was determined by vapor pressure osmometry, high pressure liquid chromatography (HPLC), and gel permeation chromatography (GPC) techniques. The kinetics of the reaction has been also analyzed. (c) 2005 Wiley Periodicals, Inc.