Functionalized and processable conducting polymers

Details Functionalized and processable conducting polymers Functionalized and processable conducting polymers

2001-07-13

2004-10-12

Truong, Duc (Department: 1711)

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

Synthetic resins

Nitrogen-containing reactant

C528S373000, C525S191000, C525S202000, C525S242000, C429S212000, C429S213000

Reexamination Certificate

active

06803446

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electrically conductive molecular complexes.
2. Background of the Invention
Conductive polymers (&pgr;-conjugated polymers) are potentially useful as a polymeric coating materials to impart special electrical, optical and electroactive properties to coated surfaces. When used to coat on metals it can impart protection against corrosion of the metals. See DE4334628 and U.S. Pat. No. 5,532,025. The electrically conductive form of the conducting polymers can also be coated on non-conductive surfaces to render the surface film to be electrically conductive. Examples of the &pgr;-conjugated polymers are polyaniline, polypyrrole, polyacetylene, polythiophene, etc.
The &pgr;-conjugated polymers are electrically conductive when it is doped by ionic compounds. In the electrically conductive state, the &pgr;-conjugated polymer backbone is a polycation. The positive charge on the ic-conjugated polymer backbone is the mobile charge that leads to electrical conductivity. The dopants are the counter ions that balance the positive charges. The difficulties in using conventional conducting polymers for coatings are associated with two of their properties; (1) they are unstable in their doped state and (2) they lack processability. The reason for the lack of processability comes from the fact that the conducting polymers are &pgr;-conjugated polymers. The delocalized &pgr; electronic structure leads to a stiff polymer chain and strong inter-chain attraction. Thus, the conventional conducting polymers cannot be easily dissolved, melted or blended with other polymers.
The lack of material stability comes from the fact that the ionic dopants are easily lost or segregated from the conventional &pgr;-conjugated polymers. Examples of the dopants that have been used include hydrogen chloride, p-toluene sulfonic acid, 4-dodecylbenzene sulfonic acid, and dinonylnaphthalenedisulphonic acid (Jen et al., U.S. Pat. No. 5,069,820, Dec. 3, 1991; Elsenbaumer, U.S. Pat. No. 5,160,457, Nov. 3, 1992; Cao et al., U.S. Pat. No. 5,232,631, 1993; Kinlen U.S. Pat. No. 5,567,356, Oct. 22, 1996). When these conducting polymers are exposed to heat, water, solvents and/or moisture, these molecular dopants are lost. Once the dopants are lost, the polymer loses its electrical conductivity and its electroactivity. The loss of dopants occurs either during the manufacturing process or during the service life of the coated product. In certain cases, molecular anions with bulky organic groups were used to reduce the rate of loss of the dopant.
This only slows down the rate of dopant loss, it does not eliminate the problem. Even when the dopant is not lost from the coating, the electrical conductivity can be lost due to the diffusion of dopants at a microscopic length scale. The detachment of the dopants from the ic-conjugated polymer backbone at a microscopic length scale (0.1 pm length) leads to dedoping. A microscopic scale phase segregation between the polymer and the dopants are easily promoted by heat or solvent. The molecular dopants tend to segregate from the vicinity of the polymeric chain of the ic-conjugated polymer backbone which results in a loss of the desirable properties.
A problem with the conventional &pgr;-conjugated polymers is that they are brittle, hard and solid. In coating applications, the conventional &pgr;-conjugated polymers do not adhere to the surface of the substrate. Thus the &pgr;-conjugated polymers are blended with an insulating, non-conductive resin so that the mixture could be adherent to the surface of a substrate. See U.S. Pat. Nos. 5,532,025, 5,543,084 and 5,556,518. When the conducting polymer is imbedded in a matrix of a non-conducting polymer such as epoxy resin, polyurethane, polyacrylate or alkyd binders, the rate of dopant loss is reduced in the macroscopic level (e.g. 0.1 mm length), but the problem of segregation at a microscopic length scale (e.g. 0.1~tm length) is not eliminated. The electroactive properties will show signs of degradation over a period of several months. For a number of applications, the material stability is not good enough. In addition to the problem with the service life of coatings or blends of these &pgr;-conjugated polymers, there are problems with the manufacturing process. The dopants are easily lost during the manufacturing process either because of heat or because of contact with water or polar solvents. For example, U.S. Pat. No. 5543084 disclosed a method for electrocoating a blend of epoxy and polyaniline. The conductive polymer PANI-PTSA (polyaniline doped by p-toluenesulfonic acid) was mechanically blended in aqueous solution and then electrophoretically coated on metal. From the disclosure it is evident that the anionic dopant of PANI-PTSA was lost before the &pgr;-conjugated polymer was co-deposited with epoxy. A redoping by immersing the coating in camphor sulfonic acid was needed to restore polyaniline to its electrically conductive state. It is expected that the dopants incorporated by redoping will be easily dedoped again by either heat or by exposure to moisture.
Coatings that use undoped polyaniline (emeraldine base) have been disclosed in the literature (McAndrew et al. U.S. Pat. No. 5,441,772, and Epstein et al. U.S. Pat. No. 5,824,371). These &pgr;-conjugated polymers without dopant are nonconductive because there is no charge carrier on the polymer backbone. These non-conducting polymer coatings do not have the comparable performance as a coating material. For most applications it is essential to maintain the &pgr;-conjugated polymers in the electrically conductive state. Thus it is desirable to have an electrically conductive polymer that is both processable and is stable against the loss of dopants.
An alternative to the above mentioned remedies is to synthesize a molecular complex of the &pgr;-conjugated polymer and a polymeric dopant. If the polymeric dopant is strongly bonded to the &pgr;-conjugated polymer the dopant will not be easily lost during the manufacturing process and the service life of the conducting polymer. A method was previously disclosed for synthesizing processable conducting polymers with stable dopants (Liu et al. U.S. Pat. No. 5,489,400). In this disclosure, a template-guided chemical polymerization was used to obtain a polymeric complex that contained a strand of polyaniline and a strand of a polyelectrolyte. The reaction product is a non-covalently bonded molecular complex between a conducting polymer and a polyelectrolyte. The molecular complex contains the two linear chains of the component polymers bonded in a side-by-side fashion. The complex is a double-strand synthetic polymer. When polyaniline is the conductive strand, dsPAN designates the double-strand polyaniline. Compared with the double-strand biopolymer, DNA, the synthetic dsPAN is less ordered in structure and is generally not in a helical conformation. Examples of the polyelectrolytes are poly(styrenesulfonic acid) and poly(acrylic acid). Since the two strands of polymers are bonded strongly, these polymeric complexes are stable and do not dedope easily.
The dsPAN disclosed in this '400 patent is one of three types. The first type is a water-soluble polymeric complex of polyaniline. This type of dsPAN is not suitable for anticorrosion coating applications because a pure dsPAN coating is redissolved in contact with water therefore the coating is lost in rain or humid air. It is conceivable that the water-soluble dsPAN be incorporated in a polymeric binder that prevents water dissolution of the coating. The hydrophilicity of this type of dsPAN is, however, still a problem for corrosion protection. The coating will absorb moister or swell in water thus reduce the adhesion of binder to the metal substrate.
A second type of dsPAN disclosed was an insoluble solid that precipitates from the aqueous reaction medium. This type of dsPAN can only be mixed with the binder by vigorous mechanical mixing (in a manner similar to that used for blending single-strand PANI-PTSA w

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