WO1995000882A1

WO1995000882A1 - Soluble, conductive copolymer, the preparation and use thereof

Info

Publication number: WO1995000882A1
Application number: PCT/NL1994/000144
Authority: WO
Inventors: Barteld De Ruiter; Theodorus Johannes Jacobus Maria Kock
Original assignee: Nederlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno
Priority date: 1993-06-22
Filing date: 1994-06-20
Publication date: 1995-01-05
Also published as: NL9301085A; AU6985194A

Abstract

The invention relates to a soluble copolymer which is conductive as a result of the presence of a conjugated system, which copolymer contains, in side chains, functional groups as well as groups conferring solubility, it being possible for the polymer chains to be covalently bonded to one another via the functional groups, which yields a cured copolymer network, a method for the preparation thereof, a method for the production of a conductive pattern by metallisation, preferably via an electrolytic process on a conductive pattern, and a conductive pattern obtained in this way.

Description

Soluble, conductive copolymer. the preparation and use thereof

The invention relates in particular to conductive polymers which can be used for patterns to be produced by lithographic means. In Mol. Cryst. Liq. Cryst. 189. 221-225, Angelopoulos et al. describe a lithographic process in which a soluble poly-(3- alkylthiophene) is rendered insoluble and conductive by radiation-induced doping via onium salts. However, no crosslinking of the polymer structure occurs with this method. In Synthetic Metals 41-4 (1991) 83- 92, Zinger et al. describe the chemical and electrochemical properties of a number of polythiophenes. They report that new chemical and physical properties can be imparted to conductive polymers by incorporating a suitable functional group in the polymer. In order to maintain a high conductivity for the polymer, the functional group must be placed "away" from the conjugated system. Thiophene is mentioned as a suitable candidate. For example, there is mention of the electrochemical polymerisation of 2-(3~thienyl)- ethyl acrylate. This homopolmerisation is difficult to achieve. The invention relates to a soluble copolymer, which is conductive as a result of the presence of a conjugated system, which copolymer contains, in side chains, functional groups and groups conferring solubility, it being possible for the polymer chains to be covalently bonded to one another via the functional groups, which yields a cured copolymer network. The material according to the invention is exceptional because of the following aspects:

1. the material in question is soluble, which has great advantages when it is used in lithographic processes: following crosslinking of the soluble material, material which has not been crosslinked is washed out easily with solvent; this aspect will be discussed in more detail below;

2. in contrast to, for example, the abovementioned publication by Zinger, the material in question is a copolymer and not a homopolymer; 3- the copolymer contains both functional groups, which lead to the copolymer network, and groups conferring solubility, which yield the property mentioned under 1. The combined presence of functional groups and the groups conferring solubility is thus a special feature.

It is preferable for the copolymers according to the invention to contain, on average, 0.1-50, preferably 1-20, functional groups as well as 1-95, preferably 30-49, groups conferring solubility, per 100 double bonds. In general, the number of groups conferring solubility will therefore be greater than the number of functional groups.

If less than, on average, 0.1 functional group is present, crosslinking of the copolymer will not be readily possible. A number of functional groups in excess of 50 per 100 dquble bonds can give rise to problems relating to an undesired, premature polymerisation.

The number of groups conferring solubility is dependent on the solvent in which it is desired to dissolve the copolymer and - of course - on the nature of the groups conferring solubility. If less than 1 group conferring solubility is present per 100 double bonds, the solubility will be too low for practical purposes (lithographic processes). A number of groups conferring solubility in excess of 95 Per 100 double bonds in general has no advantageous effect.

In particular, the functional groups present in the copolymer according to the invention can enter into linking reactions on irradiation with light, UV, gamma radiation or electron radiation. Within the framework of the present invention, linking reactions of this type are also referred to as "curing" or "forming a network" or "crosslinking" .

The following examples can be given of the abovementioned functional groups: a. Groups which possess a (meth)acrylate function:

- (CH₂)_n-X-C(0)CR=CH₂ (n = 2-12; X = 0, NH; R = H, methyl)

- (CH₂)_n,-C₆ -(CH₂)_n-X-C(0)CR=CH₂ (m = 0-12, n = 0-12; X = 0, NH; R = H, methyl) b. Groups which possess a cinnamate function:

- (CH₂)_n-C₆H₄-CH=CH-C00R (n = 0-12; R = H, C^ alkyl) c. Groups which possess a vinyl ether function:

- (CH₂)_n-0-CH=CH₂ (n = 0-12)

- (CH₂)_m-C₆H_/(-(CH₂)_n-0-CH=CH₂ (m = 0-12, n = 0-12) d. Groups which possess an epoxy function:

- (CH₂)_n-0-CH₂-[CH-CH₂-0] (n = 0-12); [CH-CH₂-0] represents the epoxide 3-membered ring

- (CH₂)_n-[CH-CH₂-0] (n = 0-12). The monomers on which the copolymers according to the invention are based are selected in particular from the group comprising substituted or unsubstituted thiophenes, pyrroles, anilines, p- phenylenes, furans and (ρ)-phenylene-vinylenes. Copolymers based on, for example, thiophenes can be prepared easily and have good solubility characteristics. On the other hand, copolymers based on pyrroles and anilines frequently have an outstanding stability in lithographic applications.

The groups conferring solubility which are present as side chains in the copolymer according to the invention are preferably groups conferring solubility in organic solvents, such as alkyl, alkoxy, thioalkyl, aryl, haloalkyl, hydroxyalkyl, aroyl and ether groups, or groups conferring solubility in water, such as sulfonic acid groups. The groups conferring solubility are chosen depending on the solvent to be used.

Examples of groups conferring solubility are: alkyl groups, for example straight-chain or branched alkyl groups having 4-20 carbon atoms; in particular straight-chain alkyl groups having 6-12 carbon atoms. - alkoxy groups, for example straight-chain or branched alkoxy groups having 1-18 carbon atoms; preferably straight-chain alkoxy groups having 1-8 carbon atoms. thioalkyl groups: ditto. aryl groups, for example substituted or unsubstituted phenyl groups, having as substituents alkyl, alkoxy, thioalkyl, N0₂,

NH₂, NHR (R = alkyl, aryl), NR₂ (R = alkyl), halogen (Br, Cl, F,

I), S0₃R (R = H, alkyl, Na, K, and other salts), acyl C(=0)R (R

= alkyl, aryl), carboxyl C(=0)0R (R = H, alkyl, aryl). ether groups: 0(CH CHR0)_nR' (R = H, methyl; n = 1-12; R' = H, alkyl). haloalkyl groups: for example (CH₂)_nX (n = 2-20, X = Cl, Br,

F, I). hydroxyalkyl groups: for example (CH₂)_n0H (n = 2-20). acyl groups: for example (COR) (R = alkyl, aryl, and the other groups mentioned, as defined above).

Groups conferring solubility in water are primarily sulfonic acid groups having the general structure (CH₂)_nS0₃H (n = 2-20) and aryl groups having side groups in which sulfonic acid groups are incorporated (CH₂)„C₆H„(CH₂)_nS0₃H (m = 0-20, n *-= 0-20).

The groups conferring solubility which are present in the copolymer according to the invention provide solubility in solvents which are commonly used in the chemical industry, including the lithographic industry. The solubility of the copolymers is highly dependent on the nature of the side group and the side group can be so chosen that solubility in a specific solvent results. Alkyl groups having a longer chain than ethyl groups produce solubility in reasonably apolar organic solvents, such as tetrahydrofuran, toluene, chloroform, dichloromethane and virtually all other chlorinated solvents. They do not produce solubility in solvents such as acetone, alcohols, water and alkanes. (Thio)ether and alkoxy side groups improve the solubility to an even greater extent. The presence of special side groups such as the abovementioned sulfonic acid groups produces solubility in water. This is extremely important because, for various reasons, such as environmental and health aspects, it is becoming ever more important to work without organic solvents.

The invention relates in particular to a copolymer, selected from the group comprising polythiophenes and polypyrroles, in which, per 100 double bonds, 2-10 acrylate ester groups, which are optionally bonded via a spacer to the main chain of the polymer, are present as functional groups and 40-48 alkyl groups are present as groups conferring solubility. There are thus 2-10 acrylate ester groups and 40-48 alkyl groups per 100 double bonds, or 4-20 acrylate ester groups and 80-96 alkyl groups per 100 pyrrole or thiophene units.

The invention relates even more particularly to a copolymer which is a polythiophene having essentially one side group per thiophene unit, 5-15 -alkylene-0(0)C-CH=CH₂ side groups and 8 -95 alkyl side groups being present per 100 thiophene units, the alkylene group having 2-12, preferably 2-4, C atoms and the alkyl group having 4-20, preferably 6, 8, 10 or 12, C atoms.

As already mentioned, the copolymers according to the invention, which are soluble in a desired solvent, can, for example, be used to form fine patterns via a photolithographic process. These patterns can be made either permanently conductive (via the presence of a resistant doping agent) or easily reversibly conductive.

Advantages of the copolymers according to the invention are: a) The polymer chains of networks formed from the copolymer are covalently bonded to one another via the functional groups, so that no leakage can take place. This increases the stability compared with that of the systems in which the polymers are not covalently bonded to the network. Moreover, no demixing problems are to be expected. b) Great versatility. The materials according to the invention can comprise virtually all conceivable types of conductive polymers. c) High degree of controllability. The degree of crosslinking can be adjusted by varying the ratios of the reagents during the copoly erisation. The levels of conductivity (or other physical or mechanical properties) can be changed (lowered) by, for example, adding conventional acrylates. In addition, variations can be made by changing the irradiation conditions. d) The copolymers according to the invention can be used in conventional processes. Many known lithographic processes are carried out using acrylate-containing materials and the particular chemical characteristics are therefore known to the users. e) A directly conductive pattern is obtained by, for example, using a combination of an onium salt and an acrylate. The system essentially has two mechanisms by which insolubility is generated via irradiation, that is to say that, respectively, doping and crosslinking takes place, whereas in the case of known methods only one mechanism is used, that is to say, in general, doping. The copolymers according to the present invention lead to a higher resolution. Free doping ions can migrate between the time of irradiation and the time of development, that is to say the washing out of soluble material. If crosslinking also occurs at the same time as doping, it is anticipated that the exposed part will have much greater dimensional stability.

For practical applications, the number-average molecular weight of the copolymers according to the invention is between, for example, 5 000 and 200 000.

The invention also relates to a method for the preparation of the abovementioned copolymers, which are soluble and conductive, in which method a monomer A containing functional groups, which yields a conductive polymer on polymerisation, is copolymerised with another monomer B, which likewise yields a conductive polymer but does not contain functional groups but, instead of the latter, contains groups conferring solubility. Because it is generally desirable that the number of functional groups in the copolymer according to the invention is smaller than the number of groups conferring solubility, in general a smaller amount, in terms of weight, of monomer A than of monomer B will be used. Preferably:

1 - 49 parts by weight of A and 99 - 51 parts by weight of B, in particular 5 - 25 parts by weight of A and 95 - 75 parts by weight of B are used per 100 parts by weight of the final conductive polymer.

The polymerisation according to the invention is, for example, carried out in a solvent and in the presence of a conventional oxidising agent, for example iron(III) chloride. The temperature during the polymerisation will in general be between 0 and 65°C, preferably 15-30°C. In particular, the polymerisation according to the invention will be carried out over a period which is shorter than the polymerisation times customary hitherto, which often are 1 or more hours. In particular, the polymerisation reaction in the method according to the invention will be allowed to take less than 30 minutes, preferably less than 15 minutes and in particular less than 10 minutes.

The polymerisation according to the invention can, for example, be carried out using the following reagents (oxidising agents):

Iron(III) salts, such as iron chloride [FeCl₃], iron nitrate [Fe(N0₃)₃] and iron perchlorate [Fe(C10_/,)₃], copper(II) salts, such as copper chloride [CuCl₂], copper perchlorate [Cu(C10₄)₂], and copper trifluoromethylsulphite ("copper triflate") [Cu(0₃SCF₃)₂] and salts of other transition metals, such as ruthenium chloride [RuCl₃] and molybdenum chloride [MoCl₅].

In addition, it is also possible to use oxidising agents which do not contain metals, such as ammonium persulfate [

potassium persulfate [K₂S₂0₈] and hydrogen peroxide [H₂0₂], in the presence or absence of catalysts such as Fe^2* ions. The halogens, preferably iodine [I₂] and bromine [Br₂], can also be used as oxidising agents.

Solvents suitable for carrying out the polymerisation according to the invention which may be mentioned are: Chlorinated hydrocarbons, such a chloroform, and dichloromethane, and also polar solvents, such as acetonitrile, nitrobenzene and propylene carbonate. Water can also be used as the reaction medium. The method described above is outstandingly suitable for the preparation of the copolymers according to the invention. It has been found that electrochemical polymerisation of suitable monomers, for example thiophenes, is not very suitable for the preparation of appreciable amounts of polymer product, whilst irregular polymer chains (for example a large amount of 2,4 linkages) are also obtained. It is, however, also possible to prepare the soluble, conductive polymers according to the invention in another way. With this method, a polymer is first prepared which essentially does not contain the functional groups which can enter into linking reactions but does contain the groups conferring solubility. The functional groups are then introduced via a chemical reaction. Of course, it will possible to introduce the functional groups into the polymer only if suitable points of attachment are already present.

The invention also relates to a method for the preparation of a polymer network by irradiation with light, UV, gamma radiation or electron radiation of a copolymer as defined above or of a mixture which contains, in addition to a copolymer of this type, one or more additives selected from substances conferring conductivity and substances which on irradiation effect simultaneous oxidation of the copolymer and thus yield a conductive crosslinked polymer material.

The preparation of the polymer network according to the invention is preferably carried out in the presence of onium salts, which preferably are selected from triarylsulfonium and diaryliodonium salts containing PF₆ ^", SbF₆ ^", AsF₆ ^" or BF₄ ^" as counter-ion. Preferably, the aryl groups in the salts are as defined above. The presence of these salts ensures simultaneous oxidation of the polymer on irradiation and leads to a conductive material. In the absence of the salts a non-conductive material is obtained, but this can nevertheless have practical applications, for example in rechargeable batteries, re-writable offset plates, electrochromic displays and sensors.

According to a preferred embodiment of the method according to the invention for the preparation of a polymer network, onium salts which contain the same functional groups as are present in the copolymer to be crosslinked itself are likewise used, so that the functional groups of the onium salts are also integrally incorporated as doping ions in the polymer network. A photo-initiator is generally added to the material to be crosslinked when crosslinking under the influence of light or UV. The invention further relates to a method for the production of a conductive pattern on an insulating substrate, with which method a film of a copolymer according to the invention or a mixture which contains such a copolymer is applied to the insulating substrate, the film is irradiated with light, UV, gamma radiation, or electron irradiation through a template with the formation of a polymer network and the non- irradiated parts of the polymer film are removed, preferably washed out with solvent, preferably a non-toxic solvent, such as water. In addition to the copolymer according to the invention, said mixture contains one or more additives selected from substances conferring conductivity and substances which, on irradiation, effect simultaneous oxidation of the copolymer and thus yield a conductive crosslinked polymer material, as defined above.

The invention also relates to a method for the production of a conductive pattern by metallisation, preferably by means of an electrolytic process on a conductive pattern obtainable by the method described above. The metallisation of a conductive substrate proceeds in a simple manner via a conventional electrolytic process. For commercial reasons, copper-plating is to be preferred. Other metallisations which are possible are nickel-plating, chromium-plating, gold-plating, silver- plating and palladium-plating (Ni, Cr, Zn, Au, Ag, and Pd respectively). The invention further relates to conductive patterns which are obtainable according to the method of the invention described above, as well as to devices which are provided with such conductive patterns. The invention is explained in more detail in the following examples.

Example 1:

Preparation of the copolymer

3-n-Hexylthiophene (2 g) and 2-(3~thienyl acrylate) (0.5 g) are dissolved in chloroform (35 ml) and the mixture is stirred with 10 g of anhydrous FeCl₃. After 4 minutes the reaction mixture is poured out into 500 ml of methanol and the precipitate is collected by means of filtration. It is purified by means of 16 hours extraction with 500 ml of ethanol in a Soxhlet apparatus and 16 hours extraction with 500 ml of acetone in a Soxhlet apparatus and then dissolved in 250 ml of chloroform by extracting for 16 hours in a Soxhlet apparatus. After evaporation of the extract under reduced pressure, 1 g of a solid remains behind, which solid has a number-average molecular weight of about 20 000 (determined by gel permeation chromatography in comparison with polystyrene standard) and NMR characteristics corresponding to the proposed copolymer structure. The copolymer contains 88 % hexylthiophene units and 12 % acrylated thiophene units.

Example 2:

Preparation of crosslinked film

The polymer having 88 % hexyl hiophene units and 12 % acrylated units (0.15 g) and bis-(4-octylphenyl)iodonium hexafluorophosphate (0.0375 g) are dissolved in 15 ml of chloroform and the solution is poured out on to a substrate (for example a glass plate). After evaporation of the solvent, an approximately 10 μm thick film remains behind. Irradiation of this film with electron radiation (40 MRad) renders the film insoluble in chloroform. If only part of a film having the same composition is irradiated, only the irradiated part of the film becomes insoluble and the non-irradiated part can be removed with chloroform.

After irradiation, the film has a conductivity of 0.01 S/cm. If the bis-(4-octylphenyl)iodonium hexafluorophosphate is omitted when making up the film-forming formulation, crosslinking does occur during irradiation of the film, but the conductivity is < 10^"6 S/cm.

Claims

1. Soluble copolymer, which is conductive as a result of the presence of a conjugated system, which copolymer contains, in side chains, functional groups and groups conferring solubility, it being possible for the polymer chains to be covalently bonded to one another via the functional groups, which yields a cured copolymer network.

2. Copolymer according to Claim 1, wherein 0.1-50, preferably 1-20, functional groups as well as 1-95, preferably 30-49, groups conferring solubility are present per 100 double bonds.

3- Copolymer according to Claim 1 or Claim 2, wherein the functional groups can enter into linking reactions on irradiation with light, UV, gamma radiation or electron irradiation, such as (meth)acrylate, cinnamate, vinyl ether and epoxy groups.

4. Copolymer according to one or more of the preceding claims, the monomers of which are selected from the group comprising substituted or unsubstituted thiophenes, pyrroles, anilines, p-phenylenes, furans and (p)-phenylene-vinylenes.

5. Copolymer according to one or more of the preceding claims, wherein groups conferring solubility in organic solvents, such as alkyl, alkoxy, thioalkyl, aryl, haloalkyl, hydroxyalkyl, aroyl and ether groups, or groups conferring solubility in water, such as sulfonic acid groups, are present in side chains.

6. Copolymer according to one or more of the preceding claims, selected from the group comprising polythiophenes and polypyrroles, in which, per 100 double bonds, 2-10 acrylate ester groups, which are optionally bonded via a spacer to the main chain of the polymer, are present as functional groups and 40-48 alkyl groups are present as groups conferring solubility.

7. Copolymer according to Claim 6, wherein said copolymer is a polythiophene having essentially one side group per thiophene unit, 5^_

15 -alkylene-0(0)C-CH=CH₂ side groups and 85-95 alkyl side groups being present per 100 thiophene units, the alkylene group having 2-12, preferably 2-4, C atoms and the alkyl group having 4-20, preferably 6, 8, 10 or 12, C atoms.

8. Method for the preparation of a soluble, conductive copolymer according to one or more of Claims 1-7. wherein a monomer A containing functional groups, which yields a conductive polymer on polymerisation, is copolymerised with another monomer B, which likewise yields a conductive polymer but does not contain functional groups but, instead of the latter, contains groups conferring solubility.

9. Method according to Claim 8, wherein a smaller amount, in terms of weight, of monomer A than of monomer B is used, preferably 1 - 49 parts by weight of A and

99 - 51 parts by weight of B, in particular

5 - 25 parts by weight of A and 95 - 75 parts by weight of B per 100 parts by weight of the final conductive polymer.

10. Method according to Claim 8 or 9. wherein the polymerisation reaction is allowed to proceed at a temperature of O-65 °C, preferably 15-30 °C, for a period of less than 15 minutes.

11. Method for the preparation of a soluble, conductive copolymer according to one or more of Claims 1-7. wherein a polymer essentially without the functional groups which can enter into linking reactions and with the groups conferring solubility is first prepared and the functional groups are then introduced via a chemical reaction.

12. Method for the preparation of a polymer network by irradiation with light, UV, gamma radiation or electron radiation of a copolymer according to Claims 1-7 or a copolymer obtained by the method of Claims 8-10 or 11, or of a mixture which contains, in addition to a copolymer of this type, one or more additives selected from substances conferring conductivity and substances which on irradiation effect simultaneous oxidation of the copolymer and thus yield a conductive crosslinked polymer material.

13. Method according to Claim 12, wherein the additive is an onium salt and is preferably selected from triarylsulfonium and diaryliodonium salts containing PF₆ ^", SbF₆ ^", AsF_fe ^" or BF ^" as counter-ion.

14. Method according to Claim 13, wherein the onium salt contains the same functional group(s) as the copolymer to be crosslinked. 15- Method for the production of a conductive pattern on an insulating substrate, with which method a film of a copolymer according to Claims 1-7 or obtained by the method of Claims 8-10 or 11, or a mixture as defined in Claim 12 is applied to the insulating substrate, the film is irradiated with light, UV, gamma radiation, or electron irradiation through a template with the formation of a polymer network and the non-irradiated parts of the polymer film are removed, preferably washed out with solvent, preferably a non-toxic solvent, such as water. 16. Method for the production of a conductive pattern by metallisation, preferably by means of an electrolytic process on a conductive pattern, obtainable by the method of Claim 1 .

17- Conductive pattern, obtainable by the method of Claim 15 or 16. l8. Device provided with at least one conductive pattern according to Claim 17.