Water-soluble poly(ethylene oxide)-block-poly (p-phenylene vinylene) copolymer: Synthesis and characterization
Résumé
Water-soluble and photoluminescent block copolymers [poly(ethylene oxide)-block-poly(p-phenylene vinylene) (PEO-b-PPV)] were synthesized, in two steps, by the addition of α-halo-α′-alkylsulfinyl-p-xylene from activated poly(ethylene oxide) (PEO) chains in tetrahydrofuran at 25°C. This copolymerization, which was derived from the Vanderzande poly(p-phenylene vinylene) (PPV) synthesis, led to partly converted PEO-b-PPV block copolymers mixed with unreacted PEO chains. The yield, length, and composition of these added sequences depended on the experimental conditions, namely, the order of reagent addition, the nature of the monomers, and the addition of an extra base. The addition of lithium tert-butoxide increased the length of the PPV precursor sequence and reduced spontaneous conversion. The conversion into PPV could be achieved in a second step by a thermal treatment. A spectral analysis of the reactive medium and the composition of the resulting polymers revealed new evidence for an anionic mechanism of the copolymerization process under our experimental conditions. Moreover, the photoluminescence yields were strongly dependant on the conjugation length and on the solvent, with a maximum (70%) in tetrahydrofuran and a minimum (<1%) in water.