Comparison of secondary doping and thermal treatment in poly(diphenylamine) and polyaniline monitored by resonance Raman spectroscopy

Changes in poly(diphenylamine) chains primarily doped with camphorsulfonic acid (PDPA-CSA) during the secondary doping process were spectroscopically characterized. The UV-vis-NIR spectrum of PDPA-CSA treated with m-cresol showed the NIR (1100 nm) tail of the band due to free-carrier absorption, confirming the increase of polymer conductivity. Resonance Raman and ESR results showed that, during this treatment, there was a conversion of diphenosemiquinone segments into diphenoquinoid ones. These results indicated that spinless species are the free carriers in this kind of polymer, which are in contrast with those observed for PANI-CSA treated with m-cresol. The thermal behavior of PDPA-CSA was also studied by in-situ resonance Raman and ESR spectroscopies. These results also indicated a conversion of diphenosemiquinone segments into diphenoquinoid ones. New bands in Raman spectra at high temperature presented by PANI and PDPA were assigned to oxidized structures having oxazine-like rings.