Self-doped conductive polyanilines, and method of preparing them

Details Self-doped conductive polyanilines, and method of preparing them Self-doped conductive polyanilines, and method of preparing them

1993-06-11

1994-12-06

Kight, III, John

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

Synthetic resins

Nitrogen-containing reactant

528391, 528399, 525540, C08G 7300

Patent

active

053711823

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to self-doped conductive polyanilines, a method of preparing them, and their application to the field of electromagnetism. It also relates to preparing one of the materials used in obtaining said polyanilines.
Polyaniline is a polymer whose monomer units correspond to the formula: ##STR1## in which n lies in the range 0 to 1.
Two types of ring are present in polyaniline: benzene rings and quinone rings corresponding to different oxidation states represented by the variable n. In practice, three types of polyaniline are considered: the reduced form, the semioxidized form, and the oxidized form. The reduced form corresponds to 100% benzene rings (n=1), the semi-oxidized form corresponds to 75% benzene rings and 25% quinone rings (n=0.5), and the oxidized form corresponds to 50% benzene rings and 50% quinone rings (n=0). Nevertheless, the distribution and the periodicity of benzene and quinone rings along the chain is statistical. The oxidation ratio is controlled by the quantity of oxidizer added to the polymerization reaction medium.
It so happens that the semi-oxidized form, known as "polyemeraldine" and possessing as many amine groups (N--H) as imine groups (--N.dbd.), is the form which becomes the most highly conductive after hydrogen acid fixation; this operation is called "doping".
Conduction is thus obtained when the polyaniline corresponds to H.sup.+ doping. The polymer is thus conductive while the backbone is protonated. This doping is reversible, but not very stable against possible deprotonation, e.g. by washing in water or by heat treatment that evaporates the hydrogen acid.
In order to stabilize the conductivity of such polymers, proposals have been made to dope them by grafting. However, the presence of too high a number of side chains reduces conductivity by reducing contact zones between chains. The problem thus arises of the regularity with which the grafted chains are positioned so as to avoid having too high a density of grafted chains per unit length at some particular point along the chain, since that impedes conduction.
The grafting was initially performed by the action of a dopant on non-conductive polyanilines (Patent WO-8 901 694). The amine or imine sites, corresponding respectively to the benzene rings and to the quinone rings, are the sites affected by known grafting. Such grafting thus takes place only on the nitrogen atoms, and not on the rings. For example, U.S. Pat. No. 4,806,271 describes the grafting of an alkyl chain or an aryl chain with a terminal function onto the nitrogen atom. When the imine sites of the chain are grafted, they can no longer fix protons, which condition is necessary for good conductivity.
Conductive polyanilines with improved stability against deprotonation can be obtained by "self-doping", i.e. by introducing an acid function that is securely bonded to the chain.
Self-doped polyanilines obtained by alkylation of the nitrogen atom by means of chains carrying a terminal sulfonic acid function have been described (Synthetic Metals, 31 (1989), pp. 369-378). A subsequent treatment is performed on a standard polyaniline. Under such circumstances the grafting is likewise performed on the nitrogen atom.
Research efforts have thus been directed to obtaining polyanilines that are grafted on the rings, which can be achieved only by polymerizing monomers having rings that already carry acid functions.
However, polyanilines carrying short grafted chains on their rings present no differences in physico-chemical characteristics over non-doped polyanilines, in particular with respect to chain conductivity. If the polyaniline is treated with oleum, a fraction of the rings are grafted with --SO.sub.3 H, which leads to a small increase in conductivity, up to a level close to 10.sup.-3 S.cm.sup.-1 (Mol. Liq. Cryst. 189 (1990) 255).
A polymer obtained from a monomer having a grafted chain on its ring carrying a proton donor function (--COOH) has been described in U.S. Pat. No. 4,940,517, however that function is quite insufficient for doping

REFERENCES:
patent: 4806271 (1989-02-01), Yaniger et al.
patent: 4940517 (1990-07-01), Wei
patent: 5069820 (1991-12-01), Jen et al.
Haney et al, Synthetic Metals, 31 (1989) pp. 369-370.
Alix et al., Synthetic Metals, 29 (1989) pp. E457-462.
Heath's Standard French and English Dictionary, Part I, p. 714 (1962).
The Handbook of Chemistry and Physics, (46.sup.th Edition), p. D-75.
Nebergall et al, General Chemistry, D. C. Heath and Company (4.sup.th Edition), pp. 453-461.
Lancaster Chemical Catalog, pp. 222 and 1072.

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