Methods for preparing conductive polyanilines

Details Methods for preparing conductive polyanilines Methods for preparing conductive polyanilines

1996-04-15

1998-06-30

Hampton-Hightower, P.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Treating polymer containing material or treating a solid...

528210, 528422, 528480, 528503, 525540, 252500, C08F 600, C08L 7900

Patent

active

057735689

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to polymers of aniline. More specifically, the invention relates to methods for preparing polyaniline having relatively high levels of conductivity. The invention also relates to articles fabricated from the polyaniline made in accordance with the inventive methods.


BACKGROUND OF THE INVENTION

Much attention has recently been directed to polyaniline, due in large part to its excellent stability and the relatively high levels of electrical conductivity of certain of its structural forms. For example, one form of polyaniline known as "emeraldine base" or "polyaniline base" (structure (1), Y=0.5) can be protonated (doped) by dilute aqueous protonic acid such as hydrochloric acid to produce the corresponding salt (structure (2), A=Cl). This salt exhibits conductivities of about 0.001-5 Siemans per centimeter (S/cm) as a compressed powder pellet. ##STR1## Polyaniline polymers can be processed into a variety of useful shaped articles such as fibers, films, and composites thereof. For many such applications, there is a positive correlation between increased molecular weight for the polyaniline employed and the performance properties of the resultant shaped article.
Currently, problems exist in the successful use of conductive polyanilines. For instance, the conductivity of the resultant polymers is still relatively low and increased conductivity levels would greatly advance the use of these materials in various industries. Also, to some extent, the ability to process high molecular weight polyaniline in the doped form presents problems for the useful application of these conductive polymers.
Melt processing of polyaniline has proven to be ineffective due to the decomposition of the polymer prior to its softening or melting point. Therefore, considerable research has been made in the area of solvents for the polyaniline. The emeraldine base form of polyaniline has been found to be soluble in such solvents as N-methylpyrrolidinone (NMP), certain amines, concentrated sulfuric acid, and other strong acids. However, it is preferred to process the polyaniline in its doped, conductive form to avoid the process of doping the resultant polyaniline form produced from the solution.
Recent advances in the solubility of the doped polyaniline salt are summarized in Counter-ion induced processibility of conducting polyaniline and of conducting polyblends of polyaniline in bulk polymers, Cao et al., Synthetic Metals, 48 (1992) 91-97. The authors report that polyaniline can be doped to its salt form and thereafter dissolved in common nonpolar or weakly polar organic solvents. This is accomplished by doping the base polyaniline in a functionalized protonic acid generally denoted as H.sup.+ (M.sup.- -R). The resultant doped polyaniline can then be dissolved in formic acid, and DMSO. The resulting films are reported to have relatively high conductivities. No explanation for the resulting high conductivities is suggested by the authors.
A need exists in the field to develop methods for preparing relatively high conducting polyanilines from either the base or salt form solutions in which the conductivity of the polyaniline can be greatly increased by predictable processing steps. Further, additional processes that can be followed for conversion of the base into a soluble polyaniline salt are also needed to increase processing alternatives.


SUMMARY OF THE INVENTION

The present invention provides for methods of processing polyaniline in which the conductivity of the polyaniline is substantially increased by contacting it with a phenolic compound. In one embodiment, the methods are performed by contacting a substantially solid polyaniline form, which has been initially doped with a protonic acid, having a determinable conductivity, with a phenolic compound under conditions which are effective to increase the conductivity of the polyaniline while maintaining the polyaniline in either a gelatinous or solid state. Preferably, the contacting is either by wetting the polyaniline form with t

REFERENCES:
patent: 5147913 (1992-09-01), MacDiarmid et al.
patent: 5177187 (1993-01-01), MacDiarmid et al.
Cao et al., "Counter-Ion Induced Processibility of Conducting Polyaniline and of Conducting Polyblends of Polyaniline in Bulk Polymers", Synthetic Metals 1992, 48, 91-97.
Cao et al., "Solution-Cast Films of Polyaniline: Optical-Quality Transparent Electrodes", Appl. Phys. Lett. 1992, 60, 271.
Cao et al., "Magnetic Susceptibility of Polyaniline in Solution in Non-Polar Organic Solvents and in Polyblends in Poly (methyl methacrylate)", Synthetics Metals 1992, 52, 193-200.
PCT/US92/09709 "High Molecular Weight Poplyanilines and Synthetic Methods Thereof", MacDiarmid et al., Nov. 6, 1992.

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