Thermal stability of polyaniline networks in conducting polymer blends

The thermal stability of polyaniline-camphor sulfonic acid (PANI-CSA) networks in blends with poly (methyl methacrylate) (PMMA) and a low molecular weight polyester (PES ) has been studied by transmission electron microscopy (TEM) supplemented with measurements of the optical and electrical properties. The tenuous interpenetrating fibrillar network of PANI-CSA is robust and remains intact at temperatures above the glass transition temperature (Tg) and the melting point (Tm) of the host polymers (Tg~90 °C for PMMA; Tm~60 °C for PES), indicating that the phase-separated network morphology is a thermodynamically stable phase. Although deprotonation of the PANI gradually starts around 100 °C, the network morphology persists (with crystallites of CSA, released by the deprotonation, distributed within the network). After exposure to increasingly higher temperatures, especially above 200 °C, the fibrils of the network coarsen, and the structure becomes more open. Complete deprotonation and degradation of the PANI are observed at temperatures above 200 °C. The conclusions from the TEM micrographs are consistent with thermal gravimetric analysis, spectroscopic data and electrical conductivity measurements.