Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Involving measuring – analyzing – or testing during synthesis
Patent
1994-07-18
1996-06-18
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Involving measuring, analyzing, or testing during synthesis
526256, 526258, 528380, 528423, 205419, C25B 300, C25B 302
Patent
active
055274340
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with the preparation of polymers which are electronically conductive, and with polymers obtained by that process.
It is known that certain organic polymeric materials may be conductive and further that certain such polymers may be reversibly and repeatedly converted between conductive and non-conductive states by the application of a potential difference across a film of the polymer. In general, available conducting polymers are coloured materials, typically weakly coloured in the non-conducting state and strongly coloured in the conducting state or vice versa.
It is known to prepare conducting polymers by electrochemical polymerization. The polymerization of pyrrole by such a process is described in the Encyclopedia of Polymer Science and Engineering, Vol 13, Wiley--Interscience, New York, 1988, pages 42-55. In such a process, the monomer is dissolved in an appropriate solvent in the presence of an electrolyte in an electrolyte cell. Electrochemical polymerization is carried out at room temperature and at a constant fixed voltage to precipitate the polymer onto an anode. However, under such conditions, coloured films tend to be produced.
In order to improve the strength, especially the elongation at break of such films, it is known to prepare a film by electrochemical polymerization of pyrrole carried out at low temperatures between 0.degree. and -40.degree. C. Such films are mechanically stretchable to provide a highly oriented film with improved conductivity; see Ogarawara et al, Mol. Cryst. Liq. Cryst. (1985), 118, 159-162.
Conducting polymers are potentially suitable for use in the form of a film applied to the windows of a building to control the flow of infra-red radiation, especially heat energy, through the windows; see U.S. Pat. No. 5,099,621.
If the film is able to prevent such flow in one of its states (for example in its conducting state) but to allow the transmission of heat energy in its other state, then loss of heat through the windows can be reduced or prevented when required, by the application of the necessary potential difference across the film. However the strongly coloured available polymers are aesthetically unsuitable for such a purpose.
There is also a potential use for conductive films in the field of infra-red photography, to generate images on substrates which are sensitive to infra-red radiation but insensitive to visual light. However films for this purpose clearly must be transparent.
There is therefore a need for a conducting polymeric material which is transparent to light in the visible range in both its conducting and non-conducting states, even if a colour change occurs in the change between those states. More preferably, the material should be colourless in both states.
Attempts have been made to produce improved conducting polymers suitable for the foregoing purposes, by synthesising novel monomeric materials from which to prepare the polymers. However the manufacture of the new monomers is both complicated and expensive and the polymers arising are relatively unstable and still exhibit colour in their conducting form.
The present invention seeks to minimise or avoid the above difficulties by providing conducting polymers having improved properties and provides a modified method of production by which this can be achieved.
Thus, the present invention provides a method of preparing a conductive polymer by electrochemically polymerizing a monomer component comprising at least one monomer in an electrochemical cell having at least an anode and a cathode, which method comprises
introducing into the cell a solution containing the monomer component and an electrolyte,
maintaining the solution at a temperature within a range of from 0.degree. to -40.degree. C. inclusive, and
repeatedly cycling an electrode potential applied to the cell between cathodic and anodic limits one of which (A) is fixed and the other of which (B) is set at a value at which anodic or cathodic polymerization takes place, thereby to effect the electrochemical polymer
REFERENCES:
patent: 5120807 (1992-06-01), Wei et al.
Polymer Communications '88 vol. 29 Jan. pp. 21-24.
Polymer '87 vol. 28 Apr. pp. 651-658.
Polymer '88 vol. 29 Aug. pp. 1522-1527.
Otero et al: "Thiophene Electropolymerization by Cyclic Voltammetry: Temperature Influence", Polymer Communications, vol. 29, Jan. 1988, pp. 21-24.
Otero et al: "Formation and Modification of Polypyrrole Films on Platinum Electrodes by Cyclic Voltammetry and Anodic Polyermication", Polymer, vol. 28, Apr. 1987, pp. 651-658.
Otero et al: "Electrochemical Generation of Polythiophene Films on Platinum Electrodes", Polymer, vol. 29, Aug. 1988, pp. 1522-1527.
Christensen Paul A.
Hamnett Andrew
Read Daniel C.
Niebling John
The University of Newcastle Upon Tyne
Wong Edna
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