Stability of MEH-PPV: Poly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene]vinylene} in solutions exposed to air in the dark and at daylight at laboratory temperature

Abstract

The long-term stability of poly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene]vinylene} (MEH-PPV) in solutions exposed to air at daylight and in the dark at room temperature has been studied using the size exclusion chromatography (SEC), UV/vis, fluorescence and IR spectra of aged samples, and comparison of UV/vis spectra of SEC fractions. Solvents currently used in the preparation, analysis and processing of MEH-PPV were used: tetrahydrofuran (THF), chloroform (CHCl3) and chlorobenzene (PhCl). The SEC-DAD data revealed a serious decrease in the delocalization of electrons in MEH-PPV chains, even in the large ones, which proves a deep damage to the structure of the chains prior to their cleavage. The IR spectra of aged samples show that the saturation of main-chain double bonds and the changes in the substitution of phenylene rings are the main chemical structure defects present in chains of aged MEH-PPV. The rate as well as the extent of the overall degradation process is ca ten to fifty times enhanced by the ordinary daylight. The rate of cleavage and the damage to the structure of MEH-PPV molecules are significantly influenced by the choice of the solvent; they increase in the order: PhCl < CHCl3< THF. PhCl can be recommended as one of the best solvents for MEH-PPV processing from solutions.