Dispersible intrinsically conductive polymer and process for its

Details Dispersible intrinsically conductive polymer and process for its Dispersible intrinsically conductive polymer and process for its

1995-11-17

1998-02-24

Lieberman, Paul

Compositions

Electrically conductive or emissive compositions

528210, 528422, 26433119, H01B 100, H01B 120, C08J 500

Patent

active

057209030

DESCRIPTION:

BRIEF SUMMARY
STATE OF THE ART

Known from DE-A-37 29 566 are intrinsically conductive polymers, in particular dispersible intrinsically conductive polymers in powder form which are important for industrial application. The definitions and terms contained in this published application are also used in the following and are therefore included in the disclosure.
The intrinsically conductive polymers and their dispersible forms known to date as a rule have conductivities between about 1 and 5 S/cm both in powder form and in the form of self-supporting films or non-self-supporting coatings. As is known from the publication by L. Shacklette et al., Proc. 49th SPE Am. Tech. Conf. 1991, 665 ("EMI-shielding"), a shield damping of 40 db can be achieved with these conductivities in the case of a layer thickness of 3 mm, which represents a minimum requirement for many industrial applications. Industrial applications are by their nature limited because of the conductivity of 1 to 5 S/cm (i.e. approx. 2.5.times.10.sup.0 S/cm) which hitherto it has been impossible to exceed on an industrial scale, and even in most cases on a laboratory scale, both in the case of use as pure polymers and as a dispersion in a polymer blend, and because of the associated necessary layer thicknesses of 3 mm.
There is therefore a need to increase the conductivity of intrinsically conductive polymers--not only for applications in EMI shielding. In particular, there is a need to increase the conductivity of dispersible conductive polymers, preferably polyaniline, in order to also equip the dispersions important for industrial applications (in thermoplastic or non-thermoplastic polymers, in lacquers or solvents) with higher conductivity.
In recent years considerable efforts have been made in this scientific field to achieve higher conductivities. The following processes have hitherto been used for this purpose on a laboratory scale: drawing and, subsequent to this, doping with iodine (Naarmann and Theophilou, Synthet. Met.) 22, 1 (1987). Conductivities of a few 10.sup.4 S/cm have been achieved. The process has the disadvantage that it is difficult to carry out and difficult to reproduce and leads to a conductive polymer which is not air- and oxidation-stable and cannot be further processed. conditions to give films which have a conductivity of a few 10.sup.2 S/cm. This process has the disadvantage that only self-supporting films can be produced which cannot be further processed and likewise are not sufficiently stable at higher temperatures. reported, thus first by Y. Cao et al. in Synthet. Met. 48, 91 (1992) and A. Heeger et al. in "Proceedings of the International Conference on Science and Technology of Synthetic Metals", Gothenburg 1992 (Synthet. Met. 55-57 (1993), being printed). In this process, polyaniline protonated ("doped") with HCl is synthesized, neutralized to emeraldine and protonated again with another acid, preferably camphor sulphonic acid, in the presence of e.g. m-cresol. Non-dispersible self-supporting films form which have a conductivity of approx. 1.5.times.10.sup.2 S/cm. In addition to the non-dispersibility and the great cost of the process, another disadvantage is to be seen in the fact that some of the m-cresol remains in the conductive, film-like composition, and that toxicological problems result both during the process and in later use. According to details from the authors and according to interpretations of other scientists (inter alia A. McDiarmid), the principle of the process is that camphor sulphonic acid induces a solubility of polyaniline ("Camphor sulphonic acid induced solubility of PAni") and m-cresol acts as secondary doping agent ("secondary dopant"). Investigations by A. Heeger and A. McDiarmid have shown that the crystallinity of the polyaniline is increased by the process. have already previously reported higher conductivities of approx. 10.sup.2 S/cm when neutral polyaniline films (films of emeraldine) were drawn and then doped. No wide-ranging work has however been carried out in this field.
To summarize, the dis

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