Thermal stability of polyaniline networks in conducting polymer blends

The thermal stability of polyaniline-camphor sulfonic acid (PANI-CSA) networks in blends with poly(methacrylate 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 (T-g) and the melting point (T-m) of the host polymers (T-g similar to 90 degrees C for PMMA; T,similar to 60 degrees C for PES), indicating that the phase-separated network morphology is a thermodynamically stable phase. Although deprotonation of the PANI gradually starts around 100 degrees 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 degrees 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 degrees C. The conclusions from the TEM micrographs are consistent with thermal gravimetric analysis, spectroscopic data and electrical conductivity measurements.