Polyaniline temperature

Although polyacetylene has served as an excellent prototype for understanding the chemistry and physics of electrical conductivity in organic polymers, its instabiUty in both the neutral and doped forms precludes any useful appHcation. In contrast to poly acetylene, both polyaniline and polypyrrole are significantly more stable as electrical conductors. When addressing polymer stabiUty it is necessary to know the environmental conditions to which it will be exposed these conditions can vary quite widely. For example, many of the electrode appHcations require long-term chemical and electrochemical stabihty at room temperature while the polymer is immersed in electrolyte. Aerospace appHcations, on the other hand, can have quite severe stabiHty restrictions with testing carried out at elevated temperatures and humidities. 

Fig. 1. (a) Comparison of normalised electrical conductivity of individual MWCNTs (Langer 96 [17], Ebbesen [18]) and bundles of MWCNTs (Langer 94 [19], Song [20]). (b) Temperature dependence of resistivity of different forms (ropes and mats) of SWCNTs [21], and chemically doped conducting polymers, PAc (FeClj-doped polyacetylene [22]) and PAni (camphor sulfonic acid-doped polyaniline [2. ]) [24]. 

Figure 1 Thermal oxidative breakdown of polyethylene (temperature 200°C P02 = 350 Tor stabilizer concentration 0.5 mass percent). 1-without stabilizer 2-CaO-6 3-polydii-minodiphenylmethane disulfide 4-polydiiminodiphenylsul-fon disulfide 5-polyparaoxydiphenylamine disulfide 6-po-lydimethylaniline disulfide 7-polyaniline disulfide 8-polydiiminodiphenyloxide disulfide 9-polythiosemicarbaz-ide disulfide 10-polyamine disulfide 11-polycarbamide disulfide 12-poly thiocarbamide disulfide 13-polyethylenedi-amine disulfide.

Temperature = ISOX Polyaniline disulphide concentration 0.8% by mass. 

After Little s proposal, many researchers have pursued such an exciting system in vain. Even metallic behavior was rarely seen in doped organic polymers, gels, and actuators. As mentioned in Sect. 3.4.4, MCso with linearly polymerized Ceo" exhibited one-dimensional (M = Rb, Cs) or three-dimensional (M = K) metallic behavior [144]. Recently a doped poly aniline was reported to exhibit a metallic temperature dependence for a crystalline polymer chemical oxidation of monomers grew crystallite polyaniline [329] early doping studies on polypyrrole (PFg) and poly(3,4-ethylene-dioxythiophene)X (X = PFg, BF4, and CF3SO3) prepared by electrooxidation at low temperatures also showed a metallic temperature dependence below 10-20 K (Scheme 16) [330, 331]. 

Metallic conduction has recently been observed in specially-prepared organic compounds, such as polyacetylene, polypyrrole, and polyaniline, having conductivities of the order 10 9 (ohm-cm)1 but by proper doping these conductivities can be increased to 102 (ohm-cm)-1. Some of the organic metallic systems have also been converted into the superconducting state by proper doping, but in all cases the Tc remains at very low temperature. 

Polyaniline-supported Co(II) catalyst 41 was used to catalyze the epoxidation of various alkenes under oxygen atmosphere at ambient temperature.61 63 One report61 described a synthesis of a-hydroxy- 3-aminopyrrolidine amides as potential HIV protease inhibitors (Scheme 1). In this synthesis, catalyst 41 also mediated epoxide ring opening of the epoxide intermediate by an aniline to afford the desired product. 

B. Ogorevc, and J. Wang, Solid-State pH Nanoelectrode Based on Polyaniline Thin Film Electrodeposited onto Ion-Beam Etched Carbon Fiber, Anal. Chim. Acta 2002,452, 1. A Zr02 electrode can measure pH up to 300°C [L. W. Niedrach, Electrodes for Potential Measurements in Aqueous Systems at High Temperatures and Pressures, Angew. Chem. 1987,26, 161],... 

New materials Polyaniline (PANI) shows high temperature H binding... 

One can then propose that, as for polyaniline, a heterogeneous model for conduction [27, 28] can also describe transport in PANI/SWNT below percolation. In contrast, Kaiser model describes transport above percolation with the system s metallic character reflected in a linear temperature dependence while lacking the exponential term associated with tunneling through conduction barriers [25], The... 

Several conjugated polymers such as polyaniline, polypyrrole and poly thiophene have been prepared by chemical methods using doping. The electrical conductivity of these polymers has been controlled by (i) the type of dopant, (ii) the concentration of doping, (iii) the conditions of doping (the current density, temperature of reaction, etc.)... 

Figure 167 Time for the derivative of PPV (OCiCio)-based device, ITO/polyaniline(50nm)/OCiCi0(100nm)/Ca/Al, to drop to half-luminescence of its initial value plotted as a function of temperature. The circles indicate 3 cm2 single pixel devices driven in DC. Squares indicate data for pixellated displays driven in pulsed mode (1/16 duty cycle, 200 Hz, same average luminance as DC devices). Current density for DC driven devices is 8.3mA/cm2. After Ref. 587. Copyright 1999 American Institute of Physics, with permission.

Nevertheless, there are cases in which conductivity is not governed by disorder, or at least in a less drastic way. This is the case of highly conducting polyacetylene [27]. Conductivity approaching the value of copper at room temperature has been reported, and a high value is still observed at low temperature. Recently, polyaniline with camphor sulfonic add (CSA) as the counterion has been reported to present an almost flat temperature dependence of conductivity [28]. Such examples are quite rare, but they are of major importance for an understanding of the intrinsic conduction process. 

Organic polymers attracted considerable interest for hydrogen storage when uptake capacities of 6-8 wt% were reported for polyaniline (PAni) and polyprrrole (Ppy) at room temperature [64, 65], Unfortunately, these results could not be reproduced independently, instead room temperature values of less than 0.5 wt% at pressures up to 94bar were subsequently observed for similar samples [66, 67]. 

---