Preparation of Electrically Conductive Polymeric Systems

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

The preparation of organic polymers of the polyphenylene series by oxidative coupling is described in Macromolecular Syntheses Collective 1 (1979), 109-110, and in Naturwiss. 56 (1969), 308-313. Furthermore, R. Gehm and W. Kern, Macromol. Chem. 7 (1951), 46-61, have described the preparation of polyphenylenes by a stepwise polycondensation, giving particularly uniform para-linked methyl-substituted derivatives which are not contaminated by ortho-linked or metalinked polymers. The organic polymers of the heteropolyphenylene series differ from the polyphenylenes in that they have hetero-atoms, or groups containing hetero-atoms, between the aromatic ring systems. These polymers are described, for example, in Macromolecular Synthesis 6 (1978), 45-48. The preparation of organic polymers of the polyacetylene series by polymerizing acetylene is also known and is described, for example, by Hatano in J. Chem. Soc. Japan, Ind. Chem. Sect. 65 (1962), 723 et seq., and by D. J. Berets et al., Trans. Farad. Soc. 64 (1968), 823 et seq. Additionally, a more recent publication, by H. Shirakawa et al., J. Chem. Soc., Chem. Commn. (1977), 578-580, describes the polymerization of acetylene by means of Ziegler catalysts, to give polyacetylene. The said methods give products which are completely insoluble in conventional solvents and are obtained as black, amorphous to partially crystalline materials. The polymers amenable to the process of the present invention also include the materials obtained by the method described in Ber. Bunsenges. Phys. Chem. 68 (1964), 558-567.

It is an object of the present invention to convert the conventional organic polymers chosen from the group comprising the polyphenylenes, heteropolyphenylenes or polyacetylenes, by means of additives, into electrically conductive polymers, having conductivities greater than 10.sup.-2 S/cm, and in addition to stabilize them greatly against oxidative degradation, and increase their processability, and range of applications, substantially.

We have found that this object is achieved, according to the invention, by adding to the organic polymers, chosen from the group comprising the polyphenylenes, heteropolyphenylenes and polyacetylenes, in the absence of moisture and of oxygen, from 0.1 to 95% by weight, based on the organic polymer, of black phosphorus, and from 0.5 to 25% by weight, based on the organic polymer, sodium, potassium, rubidium or cesium or their amides. In a preferred method, the Na, K, Rb, Cs or amides of these are added in tetrahydrofuran, dimethoxyglycol, nitromethane or methylene chloride, in each case in a molar ratio of the former component to the latter component of from 1:1 to 1:50, preferably from 1:2 to 1:3.

The electrical conductivities are measured in S/cm at 30.degree. C., using the method of F. Beck, loc. cit. The electrical conductivities of the novel conductive polymers are greater than 10.sup.-2 S/cm.

Using the process according to the invention, from 0.1 to 95% by weight, based on the weight of the polymer, of black phosphorus, and from 0.5 to 25% by weight, based on the weight of polymer, of an alkali metal or of an amide thereof, is added to the organic polymers.

The additives are incorporated in the absence of moisture (water) and of oxygen (air) and the process is therefore preferably carried out under a noble gas-argon atmosphere, eg. argon. If desired, an auxiliary fluid such as tetrahydrofuran, dimethoxyglycol, nitromethane or methylene chloride is employed, which is stripped off, after incorporation of the additive, under reduced pressure at below 30.degree. C.

Increases in the electrical conductivity by several orders of magnitude can be achieved by means of the additives stated. The initial conductivity of the organic polymers is less than 10.sup.-12 S/cm, but after incorporation of the additives according to the invention the conductivities are greater than 10.sup.-2 S/cm.

The electrically conductive polymeric systems prepared according to the invention and having conductivities greater than 10.sup.-2 S/cm may be used for the antistatic treatment of plastics, for the production of solar cells, for conversion and fixing of radiation, and for the production of electrical and magnetic switches. The addition of the alkali metals or of their amides and of black phosphorus results in n-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.

In each case, the additive in question is added to 10 parts of an organic polymer under an argon atmosphere, with exclusion of moisture. The electrical conductivity is measured by the method of F. Beck, loc. cit.