Enhanced thermal stability of polypyrrole hexagonal microplates fabricated by organic crystal surface-induced polymerization

Abstract

The stability of polypyrrole hexagonal microplates (PHMs) fabricated by organic crystal surface-induced polymerization (OCSP) in the presence of 4-sulfobenzoic acid monopotassium salt (SBAK) crystals was examined during thermal aging at 150°C for 10h under air and nitrogen atmospheres. Thermal stability of PHMs and conventional polypyrroles (CPPys) was evaluated in terms of the resistivity (Rt) after aging for t h, normalized to the initial resistivity (R0) before aging, Rt/R0. Although the PHMs maintained R10/R0 values of 21.9 and 3.0 under air and nitrogen, respectively, the CPPys exhibited much higher R10/R0 values, of 853.8 and 14.6, respectively. A possible explanation for the enhanced thermal stability of the PHMs is the higher thermal stability and the antioxidant effect of SBAK dopant molecules. Thermo-oxidative degradation was accelerated due to direct chemical attack on the cationic pyrrole rings of atmospheric water and oxygen, leading to a steep increase in surface resistivity. The development of carbonyl defects on PPy chains during thermal aging was monitored using Fourier transform-infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Ultraviolet?visible (UV?vis) spectroscopy revealed that the PHMs essentially retained the bipolaron structures, even after thermal aging for 10h in air, whereas the CPPys showed almost no bipolaron structures.