Study of the thermal elimination and degradation processes of PPV and OC(1)C(10)-PPV (precursor) polymers with in-situ analytical techniques

The synthesis of the conjugated material is performed via available precursor routes, in which the conjugated polymer is obtained by a thermal elimination step at the end of the process. Sulphur containing functional groups, for instance sulphinyl or xanthate groups, will be used in the thermal conversion step. It is to be expected that the quality and morphology of the final conjugated material will strongly depend on the elimination reaction. Therefore, insight in the elimination process and in the occurrence of side reactions is of utmost importance. In order to monitor the elimination reaction of precursor polymers, several in-situ analytical techniques are combined (TGA, DIP-MS, in-situ FT-IR and UV-Vis spectroscopy, MTDSC,…).; From in-situ FT-IR and UV-Vis experiments, we can conclude that the elimination reaction of n-alkyl-sulphinyl-PPV and -OC₁C₁₀-PPV precursor polymers starts around 65°C and 70°C respectively (heating rate: 2°C/min). These polymers stay stable till 350°C and 230°C respectively. Above these temperatures, degradation occurs, implying that the effective conjugation length irreversibly decreases. After elimination of the OC₁C₁₀-PPV precursor polymer, a certain amount of elimination products, which are set free during the elimination reaction, remain in the polymer matrix, while in pure PPV, the elimination products are ejected more extremely from the polymer matrix. When the elimination reaction is performed in vacuum conditions, the elimination reaction shifts to lower temperatures. Non-isothermal heating experiments at different heating rates, yield a valuation for the activation energy of the conversion reaction. From isothermal elimination reactions studied with in-situ FT-IR and UV-Vis spectroscopy, an activation energy of 100 kJ/mol and 92 kJ/mol for the n-butyl-sulphinyl-OC₁C ₁₀-PPV precursor polymer, was obtained respectively.; Also MTDSC is used to study the elimination process of _n-alkyl-sulphinyl-OC ₁C₁₀-PPV precursor polymers. From a combination of isothermal and non-isothermal MTDSC experiments in solid state, we could say that the elimination process is a combination of consecutive reaction steps, which are difficult to separate. MTDSC is a good technique to study the disproportionation reaction, which occurs in a temperature range between 85 and 135°C. After 150°C, side reactions occur through interaction of the elimination products with the conjugated polymer. Therefore it is better to do the elimination reaction at relative low temperatures (<120°C) and in solution. Studying the elimination process with MTDSC in solution, yields an indication for phase-separation.; Also the elimination behaviour of a xanthate PPV precursor polymer is studied with in-situ analytical techniques. The elimination of a xanthate PPV precursor polymer towards a conjugated PPV polymer when performed beneath 195°C will lead to a mixed cis-trans configuration. To obtain an all-trans PPV structure the conversion should be done at a temperature around 250°C.