Antioxidative Dopant for Thermal-Resisting Polypyrrole and Its Mechanism

Abstract

In order to improve the thermal stability of the electric conductivity of polypyrrole (PPy), a series of aromatic sulfonate derivatives having acid-type substitute groups, such as –COOH, –OH, and –SO3H, were used as dopants. The PPy doped with these dopants showed excellent thermal stability of their electric conductivity, even at 150 °C in air. Especially, 2-hydroxy-5-sulfobenzoic acid, having one –COOH and one –OH, provided the highest thermal stability; the doped PPy maintained 95% of its initial conductivity, even after heating for 8 h at 150 °C in air. Furthermore, the PPy showed 20-times higher stability against long-term heating at 125 °C for 1000 h in comparison with PPy doped with p-methylbenzenesulfonic acid, which is conventionally used to provide high thermal stability. The thermal-stabilization mechanism has suggested that dopants having acidic substituents should suppress proton dissociation from the N-position of the PPy main chain and keep the π-conjugation structure by supplying a proton from the acidic groups. Such a proton supplement was confirmed by the IR spectroscopy of deuterized PPy.

Comparison of surface and bulk doping levels in chemical polypyrroles of low, medium and high conductivity

“…During PPy degradation, the formation of HCl should be a reaction of the dopant, the chloride anion and the labile hydrogen of the polymer chains (-NH-groups) according to Scheme 3. According to this degradation mechanism, at high temperatures, proton dissociation from the N-positions of the PPy main chain occurs 41 leading to hydrogen chloride evolution and disruption of -conjugation along the chain. The strong acidic nature of the evolved HCl gas from PPy samples at elevated temperatures was confirmed by direct pH measurements.…”

Electrostatic Adsorption Behaviors of Polymer Plates to a Droplet

“…The successful PPy coating was confirmed by a visual change in appearance from transparent to black. The SO 3 – groups on the PET plate surface could work as an effective dopant for PPy, allowing for a strong electrostatic binding of the PPy shell to the plate. − On the surface of the PPy-coated PET plates, submicrometer- and micrometer-sized particulate roughnesses, which were not present on the PET plates uncoated with PPy shell, were observed. This surface roughness should be introduced by the adsorption of PPy homopolymer particles that were produced in the bulk aqueous medium, as reported previously. ,, The PET-PPy plates hydrophobized with C 8 F dopant have side lengths of 0.99 ± 0.03, 0.98 ± 0.01, and 1.00 ± 0.01 mm ( n = 6) and edge thicknesses of 13.5 ± 1.1, 23.7 ± 1.8, and 69.5 ± 2.9 μm ( n = 6), respectively, which were similar to those of original PET plates.…”

Polymerising pyrrole on polyester textiles and controlling the conductivity through coating thickness

“…The longer heating time and higher temperature result in increase charging on the sample surface. The loss in conductivity was attributed to oxidation and deprotonation at N-atom of the pyrrole ring [25][26][27][28]. Some parts of the coating was found to be considerably damaged by heat treatment, which manifested as electrical charging on the fibre surface as seen in the SEM images in Fig.…”