A comparative study of polyaniline films using thermal analyses and IR spectroscopy

The authors used dynamic mechanical and dielectric thermal analyses together with infrared spectroscopy to identify molecular motions in polyaniline films cast from emeraldine base powder dissolved in the solvent N-methyl-2-pyrrolidinone (NMP). These relaxations include a librational ring motion at around -80 degrees C and a glass transition (T_g) centred at 100 degrees C. They have also observed a permanent film hardening process at around 180 degrees C which is ascribed to polymer chain crosslinking, both physical (associated with chain entanglements) and more importantly chemical (chain-chain chemical bonding). Chemical crosslinking can be further identified with chain defects and residual impurities in the polymeric material. The importance of precise control of polyaniline synthesis and processing is therefore strongly emphasised. These results have clear implications for the thermal orientation process in polyaniline.