AU596192B2 - Electroconductive polymer-latex compositions - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: This cent glneadnents made undr Sectin 49.

and ig me,,j tor print,24 APPLICANT'S REFERENCE: 31,764-F Name(s) of Applicant(s): The Dow Chemical Company Address(es) of Applicant(s): 2030 Dow Center, Abbott Road, Midland, Michigan 48640, UNITED STATES OF AMERICA.

.Address for Service is:

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0 0 p Q+ [ILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA t" complete Specification for the invention entitled: ELECTROCONDUCTIVE POLYMER-LATEX COMPOSITIONS Our Ref 58942 POF Code: 1037/1037 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 6003q/ 1 -12- 1~ ELECTROCONDUCTIVE POLYMER- LATEX COMPOSITES The present invention relates generally to conductive polymers. Specifically, the present invention provides a polymer-latex composite comprising an organic polymeric material dispersed in a latex S which is doped to provide an electroconductive polymer- L latex composite. The latex effectively serves as a carrier for the polymeric material.

Conductive polymers are well known in the art.

They have found uses in making moldable semiconductors and active elements for electronic devices, such as, for example, active elements in electrophotographic copying machines.

Conductive polymers are generally prepared from backbone polymers, such as polyacetylene, which are made electrically conductive by molecular doping of the 20 polymer. Effective doping agents are generally strong 08 reducing or oxidizing agents. Common dopants used include p-tetracyanoquinodimethane (TCNQ), arsenic pentafluoride,.and iodine. By doping polymers with 31,764-F -1- 11- -2these dopants, nominally semiconducting or insulating materials can be made into semiconducting and metalliclike materials. Such materials provide the advantages of the low cost, light weight, moldability and flexibility of polymers along with the desirable properties of electrical conductors.

Although films of electroconductive polymers provide these advantages, they suffer from several disadvantages in certain physical properties. For example, films of polyacetylene are very thin and often brittle. Consequently, they often flake and crumble, making them unsuitable for many applications. It has also been observed that films of polyacetylene, after doping, are very sensitive to air and become nonconductive after only a few days. This is believed to 0o. be caused by oxidation of the activated polymer.

"o S What is desired is a conductive polymer that o: 20 retains its electrical properties for a longer period of time when exposed to air. In addition, it is desired to have a conductive polymer which is less brittle and therefore much more easily fabricated into a variety of film shapes.

a w25 The present invention provides a unique, o electrically conductive, polymer-latex composite comprising an organic polymeric electroconductive Smaterial, a latex capable of mixing with and dispersing o. o 30 the organic electroconductive material and a dopant.

o 0 In one embodiment of the present invention, an initially undoped organic electroconductive material in powder form is mixed with a water-based latex, then spread and solidified by drying. The resulting film is 31,764-F -3doped to provide an electrically conductive film which is non-brittle, easily fabricated into a variety of film shapes, and retains its electrical conductivity for an extended amount of time. These unique composites are useful for various applications, such as providing coatings for articles sensitive to electrostatic charges, or as catalyst electrodes.

A preferred embodiment of this invention is an electroconductive polymer-latex composite comprising from 5 to 60 weight percent electroconductive organic material and 40 to 95 weight percent styrene-butadiene or acrylic latex.

The latex component of the composite can be any .i appropriate latex material. Latex is a white, tacky 1 t aqueous suspension of a hydrocarbon polymer occurring naturally in some species of trees, shrubs or plants.

In addition, latex can be manufactured synthetically.

These elastomers are made generally by emulsion polymerization techniques from materials, such as, for example, styrene-butadiene copolymer, acrylate resins, and polyvinyl acetate. The solid, or polymer, component of a latex emulsion is also commonly referred to as latex, especially after the liquid component has baen removed.

Either a natural or synthetic latex can be i30 employed in the present invention. In a preferred embodiment of the present invention, a styrenebutadiene or acrylic latex is employed.

The organic electroconductive material of the present invention can be a variety of organic materials characterized generally as poly-conjugated unsaturated 31,764-F -3- -:i 1- i r materials. Such materials include, but are not limited to, polyacetylene, polyphenylene, polyphenylenesulfide, polysubstituted acetylenes and copolymers thereof. In a preferred embodiment of the present invention, polyacetylene is employed.

In preparing the polymer-latex composite, the organic material is first ground into a powder. The powder is then mixed with the water-based latex material. Only shaking is required to completely disperse the powder in the latex. It is believed that the polymer material occludes to latex particles to provide a stable dispersion. In this way the latex serves as a carrier for the organic material. The mixture of the originally white latex and, for example, I i black polyacetylene powder produces a composite having a bluish, metallic tint.

A variety of dopants can be employed in the Spresent invention, including but not limited to, S chlorine, bromine, iodine, arsenic pentafluoride and p-tetracyanoquinodimethane. The simplest dopants would be strong acids, such as hydrochloric acid, hydrobromic acid or similar acids.

o The method of doping the composite is not limited to any one technique. For example, if the dopant is in solution, it can be added directly to the latex and mixed. In another method, the polymer-latex S composite can be exposed to, for example, a chlorine Svapor atmosphere. In a preferred embodiment of the invention, the polymer-latex composite is spread and solidified by drying on a substrate, then exposed to an iodine vapor atmosphere.

31,764-F -4- The following examples are given to more fully illustrate the invention and shall not be construed as limiting the scope of the invention.

Example 1 Preparation of Polyacetylene Preparation of polyacetylene was conducted as follows: Sodium borohydride (0.1442 g) was dissolved in 50 ml of isopropanol and the solution cooled in a dry-ice/acetone bath to -75 0 C. A 1 weight percent solution (1.5 ml) of Co(N0 3 2 in ethanol was added.

Acetylene gas was added to the solution and the dark, brown to black polyacetylene began to immediately precipitate. The mixture was filtered and the black polyacetylene powder was washed with isopr.panol and then dried.

Example 2 Demonstration of Conductivity of a Styrene- Butadiene Latex Poly(acetylene) Composite The polyacetylene powder prepared according to Example 1 was dispersed in an aqueous styrene-butadiene j latex, spread as a film and allowed to dry overnight in air. The dried film was then placed in a jar ",25 containing a single crystal (1 g) of 12 and allowed to stand overnight in the 12 vapor. Pressing the leads of a digital ohm meter into the treated film -resulted in a current flow and a resistance measurement in the 5 to S3 10 megaohms range.

A t" 3 0 Example 3 Preparation of Polyacetylene Preparation of polyacetylene was conducted as follows: To a mixture of 1600 cc of toluene, 64 cc of a 25.1 weight percent AlEt 3 in toluene and 1.6 cc of Ti(OBu) 4 was added acetylene gas at room temperature.

31,764-F i 1 II :r -6- The black precipitate which formed was filtered and washed with copious amounts of toluene to remove the catalyst. The resulting black powder was then dried.

S Example 4 and Comparative Runs B, C and D Comparison of Conductivity of Poly(acetylene) Film Alone and Latex-Poly(acetylene) Composite Film To 1.0 g of the polyacetylene prepared according to Example 3 was added 9.0 g of Dow Latex 620, which is a 50 weight percent aqueous emulsion of a styrene-butadiene polymer. The mixture was shaken until a uniform dispersion was obtained. This mixture was spread on a microscope slide, and allowed to dry overnight.

Similarly, Dow Latex 620 containing no polyacetylene was spread on a microscope slide and polyacetylene powder sifted onto the surface. After drying overnight, this provided a film of the I polyacetylene alone not dispersed in the polymer). This slide was labeled Comparative Sample D.

Similarly, Dow Latex 620 alone was spread on a 1 25 microscope slide and used as a control. This slide was labeled Comparative Sample C.

The three slides were placed in an 12 vapor atmosphere overnight. The next day the electrical conductivity of each was measured using the 4-probe method described by L. Valdes, Proc. I.R.E. 42, 420 (Feb. 1954), for such conductivity measurements on semiconductors. They were also measured the following day to compare the samples with respect to the amount of conductivity retained on aging. The results are depicted in Table I.

31,764-F -6- -7- Table I Example and Time, Cond cti ity, Conductivity Comparative Hr. ohm- cm- Retained Runs 4 0 4.48 x 10- 24 3.577 x 10- 5 79.8% C* D 0 1.793 x 10- 5 24 3.322 x 10- 6 18.5% Comparative Sample was non-conductive.

Example 5 Use of Poly(acetylene)-Latex Composite as *an Electrode Catalyst Polyacetylene prepared according to Example 3 (3.38 g) was mixed intimately with Dow Latex 620 (8.22 g) to give a uniformly dispersed paste-like material which had a bluish sheen in color. This material was used as an electrode catalyst in the following manner: The paste was applied by brush onto a 1.5 cm x 4 cm silver screen (40 x 40 mesh 0.010 inch (0.254 mm) wire), filling the holes and coating the surface. The resulting electrodes were allowed to dry for a few days. One electrode prepared in this I manner was doped with iodine by a procedure described 30 by P. J. Nigrey, et al., in Journal Chemical Society Chemical Communications, 594 (1979). This involved using it as an anode in a 0.5 molar potassium iodide solution (200 ml) for 30 minutes at a cell voltage of 9 volts. The doped and undoped polyacetylene electrodes were tested as cathodes along with a silver screen 31,764-F -7- J- 7?lrrY~1 tCIII_ I CI1. -8electrode and a platinum screen electrode in a 2 molar sodium hydroxide aqueous catholyte at 250C. A standard cell with a NAFION 324 ion exchange membrane separator (manufactured by DuPont), platinum screen anode, and 2 molar sodium hydroxide anolyte at 25°C was used to conduct cyclic voltametry studies. The cathodes were cycled between -0.9 volts and -1.6 volts versus a saturated calomel reference electrode, S.C.E., while current-voltage graphs were recorded. The cathodes were pre-electrolyzed for 3 minutes at volts to clean any Ag 2 0 from the silver surface.

Afterwards, the cyclic voltamographs were recorded at a scan rate of 2 millivolts per second. The current posted at a given cathode potential is representative of the catalytic nature of the electrode; more .0 current means a better electrocatalyst. The results S are depicted in Table II.

Table II 2 SCathode Materials Current Milliamps/Centimeters at -1.4 -1.5 -1.6 volts vs. SCE Undoped polyacetylene 0 1.5 Iodine doped polyacetylene 1.5 4.5 16 "o Silver 1 2 4 Platinum 7 26 100 30 This data shows that undoped polyacetylene is not an electrocatalyst -for the hydrogen evolution reaction in a sodium hydroxide electrolyte. The small amount of current flow observed is apparently due only to interaction at that fraction of the silver surface to which the electrolyte may permeate the coating and migrate. However, iodine-doped polyacetylene exhibited 31,764-F -8il- I -9much greater activity over silver. In this case the reaction is apparently taking place only at the polyacetylene surface. None were as good as platinum, which is reported to be one of the best electrocatalysts for this reaction. However, use of platinum is often prohibitive due to its cost.

Also, materials other than silver may be used as supports for the conductive polymer/latex composites of the invention. Thus, the use of good electrical conductors such as, for example, copper, steel, and conductive carbon is also contemplated. The conductor in this context serves as a current collector.

1« 4 31,764-F -9-

Claims (12)

1. An electrically conductive polymer-latex composite comprising (a) a poly-conjugated unsaturated organic polymeric electroconductive material t 4 4 I, t FY Th cl.imc defining the invention arc as f- 4 iOws 1. An electrically conductive pol -latex composite compris'ing: a poly-c jgated unsaturated organic ymeric material capable of being doped to proyjde an organic electroconductive a latex into which the organic polymeric material is dispersed; and a dopant. I I I 1141: 414 .4~ I I If S2. A composite as claimed in Claim 1 wherein the organic polymeric material is selected from polyacetylene, polyphenylene, polyphenylene-sulfide, polysubstituted acetylenes and their copolymers and is present in an amount of from 5 to 60 percent, based on the total weight of the organic polymeric material and the latex.

I

3. A composite as claimed in Claim 1 or Claim 2 wherein the latex is a styrene-butadiene latex, acrylic latex or natural latex and is present in an 31,764-F 1 -11- amount of from 40 to 95 percent based on the total weight of the organic polymeric material and the latex.

4. A composite as claimed in Claim 1 wherein the latex is a styrene-butadiene or acrylic latex; the organic polymeric material is selected from polyacetylene, polyphenylene, polyphenylene-sulfide, polysubstituted acetylenes and their copolymers; and the dopant is selected from chlorine, bromine, iodine, arsenic pentafluoride, p-tetracyanoquinodimethane.

A method of preparing an electrically conductive polymer-latex composite comprising the steps of: mixing a poly-conjugated unsaturated organic polymeric maerial with a latex; and doping the mixture with a dopant.

6. An electroconductive polymer-latex electrocatalyst comprising: an electrically conductive substrate; a latex on the surface of the substrate; S(c) a poly-conjugated unsaturated organic polymericmaterial dispersed in the latex 30 e e .tr eondu.ti ve; and t 1< 'it a dopant in contact with the dispersion.

7. A method as claimed in Claim 5 which includes the step of solidifying the resulting mixture 31,7-64-F -11- r~in -12- to produce a solid composite or to form a film of said latex and said polymer.

8. A method as claimed in Claim 7 in which the polymer is doped by applying dopant to the surface of said solid composite or said film.

9. A method as claimed in Claim 5 which further comprises the steps of: casting a film or sheet of the mixture or dispersion; drying the cast film or sheet; and doping the organic polymer with a dopant selected from chlorine, bromine, iodine, arsenic pentafluoride and p-tetracyano- quinodimethane.

10. A method as claimed in Claim 9 wherein the S. organic polymeric material is selected from polyacetylene, polyphenylene, polyphenylene-sulfide, polysubstituted acetylenes and their copolymers, and is I 0 present in an amount of from 5 to 60 weight percent and 4 0 125 25 the latex is present in an amount of from 40 to weight percent, all percentages based on the total k *r weight of the organic polymeric material and the latex. DATED. 22 June 1997 30 PIILLIPS ORMONDE FITZPATRICK (W C Attorneys for:- 31,764-F -12- I, -e m -Prslarr~--r~-~ -~aa~am~

11. A composite as claimed in claim 1 substantially as hereinbefore described with reference to any one of the Examples.

12. A method as claimed in claim 5 substantially as hereinbefore described with reference to any one of the Examples. DATED: 6 February 1990 PHILLIPS ORMONDE FITZPATRICK Attorneys for: THE DOW CHEMICAL COMPANY 4 £r 4: 4 4. 4 4 4 C C