Isothermal elimination of n-alkylsulfinyl OC1C10-PPV precursor polymers studied with FT-IR, UV-vis, and MTDSC: Kinetics of the elimination reaction

Abstract

The conversion of n-alkylsulfinyl OC1C10-PPV precursor polymers to the conjugated OC1C10-PPV polymer and the subsequent reactions of the elimination products in the solid state are studied in situ with FT-IR, UV-vis spectroscopy, and modulated temperature DSC (MTDSC). FT-IR and UV-vis spectroscopy allow monitoring the formation of double bonds in the conjugated system. The experimental activation energy of this conversion reaction is in good agreement with the value from theoretical modeling (101 kJ/mol). Quasi-isothermal MTDSC heat capacity measurements permit the characterization of the subsequent reaction steps of the elimination products (dimerization of sulfenic acid and disproportionation of thiosulfinate). The formation of water in the dimerization step and elimination products results in a positive reaction heat capacity (Delta C-r(p)). This increase in heat capacity is slower than the formation of double bonds, which is attributed to the fact that the dimerization and disproportionation reactions behave as consecutive reactions relative to the elimination reaction of sulfenic acid. The amount of water released in isothermal conditions can be calculated from subsequent nonisothermal MTDSC experiments and can be used as an independent measure for the extent of the dimerization reaction. Isothermal and nonisothermal MTDSC experiments in solution have shown that phase separation between the polymer and the solvent occurs. In the nonisothermal experiment a small baseline shift is visible in the heat capacity signal at high temperature, which is an indication of phase separation. In the isothermal experiments, the increase in heat capacity is larger for the elimination in solution compared to the elimination in solid state, which is also an indication not only that the increase in heat capacity is due to the elimination process itself but also that phase separation interferes beyond a certain conversion. Phase separation in isothermal conditions is also demonstrated with UV-vis spectroscopy.