Characterization of polypyrrole/polytetrahydrofuran graft copolymers by direct pyrolysis mass spectrometry

Abstract

The thermal decomposition pathways and products of pyrrole ended-polytetrahydrofuran (PTHF), p-toluene sulfonate doped polypyrrole (PTS-PPY) and polypyrrole/polytetrahydrofuran (PTS-PPY/PTHF) graft copolymers have been investigated by direct pyrolysis mass spectrometry (DPMS). The data suggest that PTHF degrade via mixed random cleavage and unzipping mechanism followed by hydrogen transfer reactions. Decomposition of dopant in the high temperature range is attributed to a strong interaction between the dopant and the host polymer, whereas the cleavage of the pyrrole ring and lack of high mass fragments are associated with a network structure. Furthermore, evolution of H 2O and CO 2 lying throughout all pyrolysis temperature range, points out the oxidation of the pyrrole units during electrolysis in aqueous media. Yet, when the trends in the characteristic polypyrrole and dopant based peaks are considered, quite high resemblance to that of pure PTS-PPY is observed. Identical products having identical time-temperature resolved ion current profiles detected at both heating rates, suggest that the thermal degradation characteristics of polypyrrole and dopant are not affected by the presence of the matrix. Significant changes in the matrix-based product peaks from the copolymer spectrum are clearly identified. Such a low pyrolysis temperature, or early appearance of product peaks in the case of ballistic heating, can be directly related to a polymer of very low-molecular weight. The only possible cause for such a trend may be the degradation of the matrix itself during electropolymerization of the pyrrole. Thus, it may be proposed that the stability of PTHF chains totally change during the electrochemical syntheses.