Method of producing &pgr;-conjugated polymers

Details Method of producing &pgr;-conjugated polymers Method of producing &pgr;-conjugated polymers

2001-11-16

2004-10-19

Kopec, Mark (Department: 1751)

Compositions

Electrically conductive or emissive compositions

Reexamination Certificate

active

06805816

ABSTRACT:

The invention relates to the preparation of &pgr;-conjugated polymers of high electrical conductivity by chemical oxidation of the complexed monomeric compounds, and to a process for the preparation of through-contacted circuit boards and multilayers.
The &pgr;-conjugated polymer class of compounds has been the subject-matter of numerous publications in recent decades. They are also known as conductive polymers or synthetic metals.
Owing to the considerable delocalization of the &pgr;-electrons along the main chain, these polymers exhibit interesting (non-linear) optical properties and, after oxidation or reduction, are good electronic conductors. These compounds will consequently probably take on a leading and active role in various practical areas of application, such as, for example, in data storage, optical signal processing, the suppression of electromagnetic interference (EMI) and solar energy conversion, and in rechargeable batteries, light-emitting diodes, field-effect transistors, circuit boards, sensors and antistatic materials.
Examples of known &pgr;-conjugated polymers are polypyrroles, polythiophenes, polyanilines, polyacetylenes, polyphenylenes and poly(p-phenylene-vinylenes). They can be prepared by various chemical and electrochemical polymerization methods (Stenger-Smith, J. D.
Prog. Polym. Sci.
1998, 23, 57-79, Feast, W. J.; Tsibouklis, J.; Pouwer, K. L.; Groenendaal, L.; Meijer, E. W. Polymer 1996, 37, 5017-5047).
For the industrial preparation of these &pgr;-conjugated polymers, chemical polymerization of the monomeric compounds is the most favourable process. Numerous problems occur in this process:
1) The low solubility of the monomeric compounds in water means that it is frequently necessary to use less environmentally friendly organic solvents, such as, for example, chloroform, methylene chloride or acetonitrile.
2) Many monomeric compounds generate an unpleasant and unhealthy odour.
3) The pure or dissolved monomeric compounds are frequently unstable on exposure to air and/or light, causing (partial) degradation to take place.
Surprisingly, it has now been found that the above-mentioned problems in the chemical polymerization of the monomeric compounds can be avoided by complexing the monomeric compounds with cyclodextrins (CDs).
The complexing of monomeric compounds with cyclodextrins and the subsequent electrochemical polymerization of the CD complexes is known. DeFeyter et al. (Chem. Phys. Lett. 1997, 277, 44-50) have investigated the &agr;-terthiophene/&ggr;-CD complex using excited dimer fluorescence in aqueous solutions. Dong et al. (Chin. Chem. Lett. 1992, 3(2), 129-132) have polymerized an aniline/&agr;-CD complex by an electrochemical method in order to exclude a certain theory relating to by-products which form in the electrochemical formation of polyaniline. Lasace et al. (Chem. Commun. 1998, 489; J. Chim. Phys. 1998, 95, 1208-1212) have reported on the electrochemical polymerization of a 2,2′-bithiophene/hydroxypropyl-&bgr;-CD complex in water.
Recently, the same group of authors has also reported on the electrochemical polymerization of a plurality of N,N-substituted dipyrrole derivatives which have been complexed with hydropropyl-&bgr;-CD (J. Chim. Phys. 1998, 95, 1196-1199).
However, none of the cited publications reports on the possibility of chemical polymerization of monomer/CD complexes. Likewise, nothing is reported on the use of these complexes for the stabilization of monomeric compounds and the very significant reduction in odour due to the complexing.
The invention therefore relates to a process for the preparation of &pgr;-conjugated polymers comprising at least the following steps:
1. complexing of a monomeric compound with a cyclodextrin, and
2. polymerization of the complexed compound using a chemical oxidant.
Examples of monomeric compounds are unsubstituted or substituted pyrrole, aniline, thiophene, vinyl and benzyl derivatives, or combinations of these compounds. Preference is given to pyrroles and thiophenes.
Particularly preferred monomers are pyrrole and 3,4-ethylenedioxythiophene (EDT).
Suitable substituents are alkyl and alkoxy groups having from 1 to 30 carbon atoms.
Suitable cyclodextrins for the preparation of monomer/cyclodextrin complexes are unsubstituted and substituted cyclodextrins.
Preferred cyclodextrins are &agr;-, &bgr;- and &ggr;-cyclodextrins and esters, alkyl ethers, hydroxyalkyl ethers, alkoxycarbonylalkyl ethers and carboxyalkyl ether derivatives thereof, or salts thereof.
Particular preference is given to methyl-&agr;-cyclodextrin, methyl-&bgr;-cyclodextrin, methyl-&ggr;-cyclodextrin, ethyl-&bgr;-cyclodextrin, butyl-&agr;-cyclodextrin, butyl-&bgr;-cyclodextrin, butyl-&ggr;-cyclodextrin, 2,6-dimethyl-&agr;-cyclodextrin, 2,6-dimethyl-&bgr;-cyclodextrin, 2,6-dimethyl-&ggr;-cyclodextrin, 2,6-diethyl-&bgr;-cyclodextrin, 2,6-dibutyl-&bgr;-cyclodextrin, 2,3,6-trimethyl-&agr;-cyclodextrin, 2,3,6-trimethyl-&bgr;-cyclodextrin, 2,3,6-trimethyl-&ggr;-cyclodextrin, 2,3,6-trioctyl-&agr;-cyclodextrin, 2,3,6-trioctyl-&bgr;-cyclodextrin, 2,3,6-triacetyl-&agr;-cyclodextrin, 2,3,6-triacetyl-&bgr;-cyclodextrin, 2,3,6-triacetyl-&ggr;-cyclodextrin, (2-hydroxy)propyl-&agr;-cyclodextrin, (2-hydroxy)propyl-&bgr;-cyclodextrin, (2-hydroxy)propyl-&ggr;-cyclodextrin, partially or fully acetylated and succinylated &agr;-, &bgr;- or &ggr;-cyclodextrin, 2,6-dimethyl-3-acetyl-&bgr;-cyclodextrin and 2,6-dibutyl-3-acetyl-&bgr;-cyclodextrin.
The mono-, di- or triethers, mono-, di- or triesters or monoester/diether substituted derivatives are generally obtained by etherification of &agr;-, &bgr;- and &ggr;-cyclodextrins using alkylating agents, such as, for example, dimethyl sulphate or alkyl halides having from 1 to 30 carbon atoms, such as, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl or octyl chloride, bromide or iodide, and/or esterification using acetic acid or succinic acid in the presence of acids.
Examples of suitable oxidants are Fe(III) salts, in particular FeCl
3
, H
2
O
2
, K
2
Cr
2
O
7
, K
2
S
2
O
8
, Na
2
S
2
O
8
, KMnO
4
, alkali metal perborates and alkali metal or ammonium persulphates. Further suitable oxidants are described, for example, in Handbook of Conducting Polymers (Ed. Skotheim, T. A.), Marcel Dekker: New York, 1986, Vol. 1, 46-57.
Methods for the preparation of the monomeric compounds are generally well known and are described in detail, for example, in Handbook of Conducting Polymers (Ed. Skotheim, T. A.), Marcel Dekker: New York, 1986, Vol. 1, 1-43; Feast, W. J.; Tsibouklis, J.; Pouwer, K. L.; Groenendaal, L.; Meijer, E. W., Polymer 1996, 37, 5017-5047, and G. Heywang; F. Jonas, Adv. Mater. 1992, 4, 116-118.
Methods for the preparation of cyclodextrins are like-wise known and are described in detail, for example, in “Römpp Lexikon Chemie” [Römpp's Lexicon of Chemistry], 10th Edition, Stuttgart/New York, 1997, pp. 845 ff., and Chemical Reviews 98 (1998) 1743-1753 and 1919-1958.
In a preferred embodiment of the invention, the complexing of the monomeric compound is carried out in a monomer/cyclodextrin molar ratio of 1:1-1.2.
The problems mentioned at the outset can be avoided by the process according to the invention. Depending on the type of cyclodextrin, it is possible to prepare more or less water-soluble complexes, which have the following significant advantages:
1) The water solubility of the monomer is drastically increased on use of one or more mole-equivalents of the cyclodextrin (for example the water solubility of 3,4-ethylenedioxythiophene can be increased by more than 30 fold using 2,6-dimethyl-&bgr;-cyclodextrin). This enables chemical polymerizations to be carried out in water with much higher monomer concentrations.
2) The odour of the monomer disappears on use of one or more mole-equivalents of the cyclodextrin since the vapour pressure is drastically reduced.
3) In its cyclodextrin-complexed form, the monomer does not discolour on exposure to air and light. This applies both to the water-dissolved complex and to the pure, solid complex.
It is n

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