The present invention relates to a process in which addition of certain bis(methyl)aryl compounds which have a further substituent other than hydrogen and on which at least one of the two methyl groups bears a leaving group, the molecular weight in the synthesis of poly(arylenevinylenes) is controlled reproducibly and can be deduced by the GILCH polymerization or by the sulfinyl precursor route, and to the polymers obtainable by means of the process according to the invention.