By introducing poly(ethylene glycol) (PEG) into the Gilch reaction system for the synthesis of soluble poly(p-phenylene vinylene)s (PPVs), significant changes were observed. First, with the involvement of PEG, the polymerization degree increases significantly and the molecular weight distribution becomes wider. The multimodial characteristic of the GPC curves at low conversions is quite evident. Second, at low PEG content, gelation dramatically disappears; with an increase of PEG, gelation reappears. From the above experimental results, the existence of various types of polymerization-active species and the anionic polymerization mechanism are confirmed, which are due to the dissociation of the carbanion-cation pairs by the complexing effect of PEG. At the same time, the enhanced dissociation of the base (t-BuO-K+) ion pairs by PEG may be responsible for the dramatic disappearance of gelation, Free t-BuO- anions have strengthened the basicity and accelerated the conjugation-formation process which competes with the interchain by-reactions. Gelation is therefore avoided.