In this paper new insights in the mechanism of the sulfinyl precursor route towards poly(phenylene vinylene) (PPV) derivatives are presented by studying the polymerisation reaction in various solvents and by evaluating the influence of both electron donating and withdrawing substituents. A strong indication is presented that in alcohols the expulsion of the leaving group is involved in the rate determining step of the reaction, the formation of the p-quinodimethane intermediate, which further also depends on the type of solvent and substituents. Moreover, two polymerisation mechanisms can occur simultaneously: a radical mechanism that results in high molecular weight polymers and an anionic mechanism yielding low molecular weights. Competition between both mechanisms strongly depends on the solvent and type of substituents. (C) 2000 Elsevier Science Ltd. All rights reserved.