Poly /polyaniline neutralization

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. 

Conjugated polymers can now claim a considerable and uninterrupted degree of attraction over a period of several decades [1]. In the initial years, research into the synthesis of the first representatives of the new substance class of conjugated polymers (polyacetylene, poly(para-phenylene), poly(parfl-phenylenevinylene), polythiophene, polypyrrole, polyaniline) was important. The resulting polymers were characterized in most cases by their insolubility and infusibility, properties that considerably hindered their structural characterization and their processing. The majority of such compounds possessed no fully defined structure and the physical properties were influenced by structural defects. Moreover, it was often difficult to distinguish between neutral molecules and the "doped" species resulting firom oxidation or reduction. 

Polyaniline films have not only been shown to exhibit electrochromism in the visible region, but also in the microwave and far-IR regions of the electromagnetic spectrum. A polyaniline film doped with camphorsulfonic add and incorporated into a sohd state microwave shutter demonstrated that the transmittance and reflectance of X-band microwave energy could be modulated [6]. At a wavelength of 10 GHz, the shutter could be switched between 4.8% transmission when the polymer is oxidized and 42% transmission when the polymer is neutral. When utilized in a reflective device configuration in combination with poly(diphenylamine), polyamline yields a high reflective modulation in the far-IR [119,120]. This device shows a reflectance contrast of 53% at 10.5 p,m, 28% at 16.5 p,m, and 46% at 620 nm. 

Substitution with an electron acceptor, such as chlorine for poly(2-chloroaniline) (33a), yields polymers that switch between yellow in the neutral form to blue in the oxidized form [122]. Sulfonic acid ring-substituted polyaniline (33b) can be prepared by direct chemical reaction of polyaniline with concentrated sulfuric acid [132]. This polymer film switches from transmissive yellow to blue even in solutions of elevated pH up to 7. 

Composites of conducting polymers, e.g., polyaniline and PEDOT, with polyacids, e.g., poly (2-acrylamido-2-methyl-l-methyl-l-propanosulfonic add) (PAMPS), have been shown to be electro-chromic. The polyadd acts as a dopant for the polymer film with the optical properties of the composite being contributed by the conducting polymer. The composites are formed by dther chemical or electrochemical polymerization of the electrochromic component monomer in the presence of the polyacid. Films of polyaniline-PAMPS switch from yellow to green and finally to blue on oxidation [228,229]. Composite films of PEDOT and PAMPS show similar electrochromic properties to PEDOT with the films switching from dark blue in the neutral state to Kght sky blue in the oxidized state [140,230,231]. 

Although most studies of corrosion protection by conjugated polymers utilize the doped (thus conducting) form of the polymer, several studies have been conducted on neutral (undoped) polymers. Most of these studies have utilized the EB form of polyaniline and include studies on A1 alloys [70,85,86], stainless steel [87], mild steel [88,89], cold rolled steel [90-92], carbon steel [93], and iron [92,94,95]. An undoped poly(2,5-bis(Ar-methyl-N -hexylamino) phenylene vinylene) or BAMPPV has been studied for the corrosion control of the A1 alloy AA 2024-T3 [96,97]. Little else appears to have been published on the use of other undoped conjugated polymers for corrosion control. 

It was also found that poly-o-pheneditine (poly-o-ethoxy-aniline) acts as a better corrosion inhibitor than unsubstituted polyaniline. With the neutral base form, the oxygen reduction and hence the metal dissolution was completely inhibited. The anodic protection in-... 

Certain polymers, such as polyaniline, in their neutral form are soluble in A/-methyl pyrrolidone (NMP) [2], A/,A/-dimethylpropylene urea (DMPU) [3], and dimethyl sulfoxide (DMSO). Films of neutral polymer can be cast from these solutions. Chemical modification of monomers has proved to be effective in enhancing the modification solubility, especially with polythiophene [4,5]. In other instances, such as poly(p-phenylenevinylene), processibility has been achieved by synthesizing solu-tion-processible precursors, which could be subsequently converted to the conjugated polymer [6]. Nonetheless these techniques have failed to provide a method... 

It has been established that, when polyelectrolytes are incorporated as dopants in polyaniline, the switch from conducting to nonconducting material is shifted to very high pH solutions, enabling electrochemistry to be carried out on polyaniline in neutral solutions. Poly(methoxyanilines) have been used as the basis of electromechanical actuators, where changes in dimensions in the thickness direction of more than 20% reported as the polymers are doped and dedoped. - Similar effects are observed if some level of self-doping is introduced into the polyaniline backbone. ... 

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