The polymerization of PPV via the sulfinyl precursor route has been investigated with respect to its mechanism. When polymerized in sec-butanol, a purely radical polymerization mechanism is observed as in most precursor polymerization routes. Accordingly, an increase in the reaction temperature induced an increase in the overall yield alongside with a reduction of the average molecular weight of the polymer. Upon changing the monomer concentration in solution before addition of the base NatBuO, an increase in molecular weight is observed, signifying that the polymerization is faster than the mixing of the two reaction components. When changing the solvent to NMP, a competition of anionic and radical polymerization has been established while in THF an anionic polymerization mechanism occurs exclusively. To prevent termination reactions, LDA and LHMDS were introduced as base whereby LHMDS shows less propensity to initiate anionic chain growth due to higher steric hindrance. With polymerizations in presence of the radical quencher TEMPO, the anionic polymerization mechanism could unambiguously be proven.

Poly(p-Phenylene Vinylene) derivatives are synthesized mostly making use of the polymerization behavior of pquinodimethane systems. Over the last forty years different synthetic routes have been developed, e.g. Wessling, Gilch, Xanthate and Sulphinyl route. For all these routes mechanistic studies are rather scarce and lead to a controversy between two possible mechanisms: anionic and radical polymerization. In this contribution it becomes clear that high molecular weight materials are associated with a self-initiated radical chain polymerization and low molecular weight materials are obtained via an anionic mechanism. This will be demonstrated for the model system in which a sulphinyl pre-monomer is polymerized in N-Methyl-Pyrrolidone. In this model system both these mechanisms are competing with each other. The observed effects on the product distribution of concentration of reagents, temperature and order in which the reagents are added, are consistent with the conclusion above. The question whether living polymerization can occur will be addressed for the radical mechanism. An experiment with a set of sequential polymerizations gives rise to an evolution of molecular weight consistent with the effect of simple dilution of the reaction medium. The conclusion is that a termination reaction is active, which can be identified as related to traces of oxygen. In these conditions the synthesis of block-type copolymers can not be achieved. For the anionic mechanism an argumentation against such possibility will be presented on the basis of relative acidities.