Preparation of Electrically Conductive Hetero-Poly-Phenylenes

The present invention relates to a process for the preparation of electrically conductive heteropolyphenylenes, having conductivities greater than 10.sup.-2 S/cm.

The preparation of polyphenylenes by oxidative coupling has been disclosed in Macromolecular Syntheses Collective 1, (1977), 109-110, and Naturwissenschaften 56 (1969), 308-313. Furthermore, the preparation of polyphenylenes by stepwise polycondensation has been disclosed by R. Gehm and W. Kern, Macromol. Chem. 7 (1951), 46-61, and this method gives particularly uniform para-linked methyl-substituted derivatives, which are not contaminated by the presence of ortho-linked or meta-linked polymers. However, the hetero-polyphenylenes according to the invention differ from the above compounds through the presence of hetero-atoms, or of groups containing hetero-atoms, between the aromatic ring systems. These hetero-polyphenylenes, on which the products according to the invention are based, are described, for example, in Macromolecular Syntheses 6 (1978), 45-48.

It is an object of the present invention to convert the last-mentioned hetero-polyphenylenes, which are known per se, by incorporation of additives, into polymers having electrical conductivities greater than 10.sup.-2 S/cm.

We have found that this object is achieved, according to the invention, by adding to the hetero-polyphenylenes, in the absence of moisture and of oxygen, from 0.5 to 35 percent by weight, based on hetero-polyphenylene employed, of a strong Lewis acid having a pk.sub.a of from -10 to +4. Preferably, the Lewis acid is AsF.sub.5, SbF.sub.5, UF.sub.6, HCl0.sub.4, NO.sup.+ SbF.sub.6.sup.-, NO.sub.2.sup.+ SbF.sub.6.sup.-, NO.sup.+ AsF.sub.6.sup.-, NO.sup.+ PF.sub.6.sup.-, NO.sub.2.sup.+ PF.sub.6.sup.-, NO.sup.+ BF.sub.4.sup.-, NO.sub.2.sup.+ BF.sub.4.sup.-, NO.sup.+ ClO.sub.4.sup.-, (CF.sub.3).sub.2 SO.sub.4, 2,4,6- trinitrophenol, 2,4,6-trinitrophenylsulfonic acid or 2,4,6-trinitrobenzoic acid.

For the purposes of the present invention, hetero-polyphenylenes are relatively high molecular weight products whose chain consists of coupled phenyl rings which may or may not carry substituents R, the products having the general formula: ##STR1## where X is S, O, NH, Se, SO.sub.2, or ##STR2## R is H, CH.sub.3, phenyl or cyclohexyl, and n is an integer from 2 to 200, preferably from 3 to 50.

Preferred hetero-polyphenylenes contain phenyl rings linked in the para-position by an S or O bridge. The hetero-polyphenylenes have molecular weights of from 800 to 500,000, preferably from 10,000 to 100,000. They may be prepared in accordance with Macromolecular Syntheses, loc. cit.

The electrical conductivities are measured by the method of F. Beck, Ber. Bunsengesellschaft, Physik. Chem., 68 (1964), 558-567, at 30.degree. C., and are expressed in S/cm. The electrical conductivities of the novel conductive hetero-polyphenylenes is greater than 10.sup.-2 S/cm.

According to the process of the invention, from 0.5 to 5 percent by weight, based on polyphenylene employed, of a strong Lewis acid having a pk.sub.a of from -10 to +4 is added to the hetero-polyphenylenes in the absence of moisture and of oxygen.

Since the additives are incorporated in the absence of moisture (water) and oxygen (air), the process is preferably carried out under a noble gas, eg. argon, atmosphere. Auxiliary fluids, such as tetrahydrofuran, dimethoxyglycol, nitromethane or methylene chloride may be employed if appropriate, and are subsequently stripped off under reduced pressure at below 30.degree. C.

By using the additives mentioned, electrical conductivity increases of about ten orders of magnitude can be achieved. The hetero-polyphenylenes used as the starting materials for the novel compositions have initial conductivities of less than 10.sup.-2 S/cm, but after incorporation of the additives according to the invention give conductivities greater than 10.sup.31 2 S/cm.

The electrically conductive hetero-polyphenylenes prepared according to the invention and having conductivities greater than 10.sup.-2 S/cm may be used for the anti-static treatment of plastics, for the production of solar cells, for the conversion and fixing of radiation and for the production of electrical and magnetic switches. The incorporation of the strong Lewis acid into the hetero-polyphenylenes results in p-conductors (cf. J. Chem. Education, 46 (1969), No. 2, 82).

In the Examples which follow, parts are parts by weight and percentages are mole percentages. The number n, ie. the chain length of the polyphenylenes, is determined by end group analysis, through infrared determination of the ratio of monofunctional terminal groups ##STR3## to difunctional non-terminal groups ##STR4##

The molecular weight may be determined, for example, from the intrinsic viscosity [.eta.], in dl/g, measured in CHCl.sub.3 at 25.degree. C. (cf. A. S. Hay, Macromolecular Syntheses Collective 1 (1977), 81).

The additive is added to 10 parts of a hetero-polyphenylene under an argon atmosphere, with exclusion of moisture. The electrical conductivity is measured by the method of F. Beck, loc. cit.