WO1999025778A1 - Synthesis and applications of intrinsically conductive polymer salts of polyphosphonic acids in anti-corrosion coatings - Google Patents

Abstract

A coating composition for protecting a corrodible metal suface from corrosion includes an intrinsically conductive salt of a polyphosphonic acid as well as a solvent and other optional components. The composition is used to form a protective coating on the surface of corrodible metals such as iron and steel. The coating passivates the metal surface and complexes the passivated metal, thus protecting the surface from rust and corrosion.

Description

SYNTHESIS AND APPLICATIONS OF INTRINSICALLY

CONDUCTIVE POLYMER SALTS OF POLYPHOSPHONIC

ACIDS IN ANTI-CORROSION COATINGS

Background of the Invention

( 1 ) Field of the Invention

The present invention relates to corrosion resistant compositions and coatings that contain an electrically conductive intrinsically conductive polymer salt, and more particularly to corrosion resistant compositions and coatings that contain an electrically conductive intrinsically conductive polymer salt of a phosphonic acid and to the preparation and applications of such compositions and coatings.

(2) Description of the Related Art

Corrosion resistant coatings for metals are designed either to form a barrier between the metal and the environment, to provide cathodic protection of the metal, as with a zinc-rich primer, and/or to passivate the metal, as with a heavy metal oxide of, for example, chromium or molybdate. Because barrier coatings are commonly breached by pin-holes and scratches and because of environmental concerns about heavy metals, there has been increased interest in protective coatings that passivate the metal surface by contact with an intrinsically conductive polymer.

Intrinsically conducting polymers (ICP's), are polymers such as polyan line, polypyrrole and polythiophene that have poly-conjugated rt-electron systems and that conduct electricity in at least one valence state. Some ICP's, such as polyaniline in its partially oxidized state, can be reversibly doped by protonic acids to form either conducting or nonconducting forms of the polymer. Usually, the ICP salts are electrically conductive, while the neutral ICP is not. It is believed that coatings that contain ICP's have conductivity properties that passivate and protect metal surfaces from corrosion, even where the coating is penetrated by pin-holes or scratches. However, the requirement of high levels of ICP's in such coatings along with the brittleness and lack of strength and adherence of films composed only of ICP's has limited their commercial application. See, for example, Deng, et al., J. Electrochem . Soc . . 136 : 2152 - 2157, 1989; Ren and Barkey, J . Electrochem . Soc , 139:1021 - 1026, 1992;

Wessling, Adv. Mater., 6:226 - 228, 1994; and Lu, et al . , Synth . Metals , 71:2163 - 2166, 1995.

ICP ' s can be incorporated into corrosion resistant coatings by applying a paint or similar composition that includes a dispersion or solution of the polymer, or by polymerization of the ICP monomer onto the surface to be protected by chemical or electrochemical means.

Formation of ICP-containing coatings by j n-situ polymerization of ICP-monomers on the surface of the metal to be protected has been disclosed by Hyodo et al. , in Electrochemical Rcta , 36:87-91, 1991; Hwang and Yang, in Synthetic Metals , 29:E271-E276, 1989; U.S. Pat. No's. 5,567,209 and 4,780,796; EP 591035; U.S. Pat. No. 4,780,796; JP 6045200 A; JP 6045199 A; U.S. Pat. No's. 4,948,685 and 4,999,263; DeBerry, J. Electrochem. Soc , 132 ( 5 ) : 1022 - 1026, 1985; Geskin, J. Chem. Phyε . , 89 : 1221 - 1226, 1992; Beck, Metalloberflaeche , 46 (4 ) : 11 - 182, 1992; Troch-Nagels, et al . , J. of Appl . Electrochem. , 22 : 156 - 764, 1992; and Li, et al . , Beijing Keji Daxue Xuebao , 13 (4 ) :367 - -372, 1991. The ICP can also be applied to the metal surface in polymeric form, such as by electrodeposition (See, e.g., U.S. Pat. Numbers 5,543,084 and 5,556,518), or incorporation of ICP's into formulated coatings, (See, e . g . , U.S. Pat. Numbers 5,494,609, 5,290,483, 5,006,278, 5,532,025, J? 5003138 A, JP 6045196 A and JP 6045195 A), and paints, (See, e . g. , U.S. Pat. No. 5,441,772 and PCT Publ. No. 093/14166).

The most common method of applying a composition containing an ICP in polymer form to a surface is in the form of a liquid coating formulation such as a paint. Carrier solvents can be evaporated to leave the ICP in the form of a coating or solid film on the surface to be protected.

Much of the prior work with corrosion resistant coatings that employ ICP's has been done with polyaniline due to its ease of manufacture, reasonable cost and ready commercial availability. Both the conductive and non- conductive forms of polyaniline have been reported to be useful in corrosion prevention and it is unclear whether one form is necessarily superior to the other. Although much of the work reported in this area suggests that the conductive form of the ICP is more effective for corrosion resistance (See, e.g., Mattson, "The Synthesis of Conducting Polymers for Corrosion Prevention", Final Report on NASA Contract NASA-NGT-60002, N89-14159, 1988; Thompson, et al. , "Corrosion-Protective Coatings from Electrically Conductive Polymers", Proceedings from Technology 2001, San Jose, Calif., 1991; and U.S. Pat. No's. 4,855,361, 5,006,278 and 5,658,649), other reports maintain that the non-conductive form is superior (See, e . g. , U.S. Pat. No's. 5,441,772 and 5,648,416). Yet other reports seem to suggest that a coating that contains polyaniline in its non-conductive emeraldine base form when first applied to a corrodible metal surface will eventually result in the polyaniline becoming doped, and therefore conductive, simply by contact with a corrosive environment. (See, e.g., U.S. Pat. No. 5,645,890). Thus, it is not apparent from the prior art which form of the ICP is most effective in all circumstances for use in corrosion resistant films and coatings.

In the work cited above in which doped polyaniline was used in anti-corrosion applications, the usual dopants were sulfonic acids. This is probably because most commercially available conducting polyaniline salts are doped with mono-functional sulfonic acids such as p- toluenesulfonic acid or dodecylbenzenesulfoni acid. These, and other aromatic sulfonic acids are known to provide high electrical conductivity to the polyaniline salt while also providing improved solubility in organic solvents. (See, e.g., U.S. Pat. No. 5,232,631 to Cao et al . and U.S. Pat. No. 5,567,356 to Kinlen). Thus, these aromatic sulfonic acid-doped polyanilines have been tested and found to be effective in anti-corrosion applications. One drawback to the use of sulfonic acid- doped ICP's, however, is that the doped polyaniline often is present in amounts that comprise over about 10% of the weight of the coating (See, e.g., U.S. Pat. No. 5,648,416), and sometimes up to 25%, or more (See, e.g. U.S. Pat. No's. 5,645,890 and 5,658,649). Moreover, although such sulfonic acid-doped polyanilines are effective in preventing some forms of corrosion on steel surfaces, in some instances they are not as effective in preventing corrosion in scratches and pinholes in the coatings and in preventing the spread of corrosion under the coating away from the scratch or pinhole. Although it is well known that almost any protonic acid can be used to dope polyaniline and form a conductive polyaniline salt, little is known about the relative anti-corrosion effectiveness of polyaniline, or other ICP's, that are doped with organic acids other than sulfonic acids and, in particular, other than aromatic mono-functional sulfonic acids. For example, phosphates and phosphonates and their complementary acids are widely used in applications for minimization of scale formation and metal corrosion in aqueous systems. Yet, little work has been reported wherein ICP's are doped with such acids. This may be because of the water insolubility of the resulting phosphonic acid-doped polyaniline salts, or simply due to the ready commercial availability of polyaniline sulfonates. In those cases where polyaniline doped with phosphonic acid has been mentioned, the focus -has been on thermal stability (See, e.g. Chan et ai . , J . Am . Chem. Soc , 117:8517 - 8523, 1995, Chan et al . , Macromolecules , 27:2159 - 2164, 1994, and Rannou et al . , Synth . Metals , S4( 1-3 ) :755-756, 1997), or electrical conductivity (See, e.g., Maia et al . , Synth . Metals , 90 ( 1 ):37 - 40, 1997, and Pron et al . , Synth . Metals , 84(1-3): 89 - 90, 1997). Although several mono-functional phosphonic acids were listed as possible dopants for polyaniline to be used in anti-corrosion coatings by Miller et al . , in U.S. Pat. No. 5,648,416, and 093/14166 only aromatic sulfonic acids were actually used as dopants for the polyaniline applied to metals to minimize corrosion.

Thus, it would be desirable to produce a composition and a coating for use in preventing corrosion on corrodible metal surfaces that was effective in preventing corrosion, and in particular in preventing or suppressing corrosion in pin-holes and scratches in the coating. Also, if such coating included an ICP, that such coating would provide anti-corrosion effective properties at reasonably low levels of the ICP.

Furthermore, it would be useful if such composition could be made to bind tightly to the surfaces of steel, or other metals to be protected.

Summary of the Invention

Briefly, therefore, the present invention is directed to an electrically conductive corrosion resistant coating composition comprising an intrinsically conductive polymer salt of a polyphosphonic acid. The present invention is also directed to a method for producing a corrosion resistant coating composition for a corrodible metal comprising mixing an intrinsically conductive polymer salt of a polyphosphonic acid and a solvent. In addition, the invention also claims a method for protecting a corrodible metal surface from corrosion, comprising applying to the corrodible metal surface a coating composition comprising a solvent and an anti- corrosion effective amount of an intrinsically conductive polymer salt of an organic polyphosphonic acid and causing a solid coating to form which coating substantially covers such corrodible metal surface. Also claimed is a coating for protecting a corrodible metal surface from corrosion comprising an anti-corrosion effective amount of an intrinsically conductive polymer salt of a polyphosphonic acid.

Among the several advantages found to be achieved by the present invention, therefore, may be noted the provision of a composition and a coating for preventing corrosion on corrodible metal surfaces that is effective despite pin-holes and scratches in the coating; the provision of a composition and a coating that include an ICP and are effective in preventing corrosion even at reasonably low levels of the ICP; the provision of a coating that can bind tightly to the surface of steel and other metals to be protected; and the provision of methods to make and use the composition.

Brief Description of the Drawings

Figure 1 is a plot of the corrosion score (which is described in detail in Example 2 ) as a function of the time of exposure to salt-fog of scribed steel panels coated with five coatings that contained polyaniline doped with different organic acids and a control that contained no polyaniline; and

Figure 2 is a bar chart showing the corrosion spread after 1500 hours of exposure to salt-fog (which is described in detail in Example 2 ) for scribed steel panels coated with five coatings that contained polyaniline doped with different organic acids and a control that contained no polyaniline.

Detailed Description of the Preferred Embodiments

In accordance with the present invention, it has been discovered that corrodible metals such as steel can be protected from. corrosion by applying an electrically conductive coating composition comprising an intrinsically conductive polymer salt of a polyphosphonic acid to the surface of the metal to be protected. A key component of such compositions and coatings is an intrinsically conductive polymer that is electrically conductive and is doped with a di-, tri-, tetra-, penta-, or other poly-functional phosphonic acid (the acid being referred to herein generally as a "polyphosphonic acid" and the doped polymer being referred to as an "ICP polyphosphonate" ) . Surprisingly, it has been found that the inclusion of such an ICP polyphosphonate provides superior corrosion protection in scratches and pinholes and superior protection against the spread of corrosion away from such scratches . The coatings that are produced by such compositions are electrically conductive and can have conductivities of over 10^"6 S/cm, and even over 1 S/cm. Furthermore, the ICP phosphonates that have been found to be preferred in this invention can be produced effectively and economically.

The subject compositions can be produced by mixing the ICP phosphonates with a solvent to provide a liquid that can easily be applied to metal surfaces. It has also been found that binders and other materials may be added to the subject compositions with the result that coatings can be produced that bind tightly to the metal surfaces to be protected. In particular, the addition of a polyvinyl butyral resin as a binder results in a composition and coating with particularly desirable properties.

The intrinsically conductive polymer salt of a polyphosphonic acid:

One component of the subject corrosionc-resistant composition and coating is the salt cf an intrinsically conductive polymer and a polyphosphonic acid. (An ICP polyphosphonate ) . The ICP polyphosphonate comprises an ICP that is protonated, or doped, by a polyphosphonic acid. ICP's useful in the present invention are formed by the polymerization of any suitable substituted or unsubstituted aromatic heterocyclic or aniline monomer. Generally, any substituted or unsubstituted aromatic heterocyclic or aniline monomer that is polymerizable into an ICP may be used in this invention. Any such monomer may hereinafter be referred to as an "ICP monomer" . The substituted or unsubstituted ICP monomers suitable for use in this invention include pyrrole and substituted pyrroles, p-phenylenes, m-phenylenes, phenylene sulfides, thiophene and substituted thiophenes, indoles, azulenes, furans and carbazoles . Aromatic heterocyclic compounds for use in the present invention include the 5-membered heterocyclic compounds having the formula:

wherein each of R^~ and R² is independently hydrogen; alkyl (e.g., methyl or ethyl); aryl (e.g., phenyl ) ; alkaryl (e.g., tolyl ) ; or aralkyl (e.g., benzyl); or R¹ and R² together comprise the atoms necessary to complete a cyclic (e.g., benzo ) structure; and X is -0-; -S-; or

R

— N — wherein R³ is hydrogen, alkyl, aryl, alkaryl or aralkyl. These materials, upon electropolvmerization, result in intrinsically conducting polymers having repeating units of the general formula:

wherein : R¹ , R² and X have the definitions set forth above . In general, substituted or unsubstituted anilines for use in this invention are of the formula:

wherein: n is an integer from 0 to 4; m is an integer from 1 to 5 , provided that the sum of n and m is equal to 5;

R^: and R⁴ are the same or different at each occurrence and are hydrogen, or are selected from R³ substituents; and R³ is the same or different at each occurrence and is selected from alkyl, deuterium, alkenyl , alkoxy, cycloalkyl, cycloalkenyl, alkanoyl, alkythio, aryloxy, alkylthioalkyl, alkylaryi, arylaikyl, aminc, alkylamino, dialkylamino, aryl, alkylsulfinyi , aryloxyalkyl, alkylsulfinylaikyl, alkoxyalkyl, phosphonic acid, alkylsulfonyl, arylthio, alkylsulfonylalkyi, borate, phosphate, sulfinate, arylsulfinyl , alkoxycarbonyl , arylsulfonyl, carboxylate, phosphonate, halogen, hydroxy, cyano, sulfinate, sulfonate, phosphmate, nitro, alkylsilane or alkyl substituted with one or more phosphonates, sulfonates, phosphates, borates, carboxylates, phosphinates , halo, nitro, cyano or epoxy moieties; or any two R^Δ groups together or any R³ group together with any R² or R⁴ group may form an alkylene or alkenylene chain completing a 3 , 4 , 5 , 6 or 7 membered aromatic or alicyclic ring, which ring may optionally include one or more divalent nitrogen, sulfur, sulfinyl, ester, carbonyl, sulfonyl, or oxygen atoms; or R³ is a divalent organic moiety bonded to the same or a different substituted or unsubstituted aniline moiety or R³ is an aliphatic moiety having repeat units of the formula:

-{—OCH₂CH₂- -0-CH3 , -—OCH₂CH( O^—^O-C^, -f-CH₂- _rCF₃, -(_CF₂- -CF₃, or _(__CH₂-^-CH₃

wherein q is a positive whole number; provided that said homopolymer and - copolymer includes about 10 or more recurring substituted or unsubstituted aniline aromatic moieties in the polymer backbone.

The following substituted and unsubstituted anilines are illustrative of those which can be used in the synthesis of polyaniline in that embodiment wherein polyaniline is the ICP component of the composition or coating: 2-cyclohexylaniline , aniline, o-toluidine, 4- propanoaniline, 2-( methylamino )aniline, 2- dimethylaminoaniline , 2-methyl-4-methoxycarbonylaniline, 4-carboxyaniline, N-methyl aniline, N-propyi aniline, N- hexyl aniline, m-toluidine, o-ethylaniline, m- ethylaniline, o-ethoxyaniline, m-butylaniline m- hexylaniline, m-octylaniline, 4-bromoaniline, 2- bromoaniline, 3-bromoaniline, 3-acetamidoaniline, 4- acetamidoaniline, 5-chloro-2-methoxy-aniline, 5-chloro-2- ethoxy-aniline, N hexyl-m-toluidine, 2-acetylaniline, 2,5 dimethylaniline, 2,3 dimethylaniline, N,N dimethylaniline, 4-benzylaniline, 4-aminoaniline, 2- methylthiomethylaniline, 4-( 2, 4-dimethylphenyl ) aniline, 2-ethylthioaniline, N-methyl-2 , 4-dimethylaniline, N- propyl m- toluidine, N-methyl o-cyanoaniline, 2,5 dibutylaniline, 2,5 dimethoxyaniline, tetrahydronaphthylaniline, o-cyanoaniline, 2- thiomethylaniline, 2, 5-dichloroaniline, 3-(n- butanesulfonic acid) aniline, 3-propoxymethylaniline, 2, 4-dimethoxyaniline, 4-mercaptoaniline, 4- ethylthioaniline, 3-phenoxyaniline, 4-phenoxyaniline, 4- phenylthioaniline, 3-amino-9-methylcarbazole, 4-amino carbazole, N-octyl-m-toluidine, 4-trimethylsilylaniline, 3-aminocarbazole, N-(paraaminophenyl ) aniline. The most preferred ICP monomer is unsubstituted aniline.

The polyphosphonic acid:

The ICP of the subject composition or coating is doped with a polyphosphonic acid. It is to be understood that when a polyphosphonic acid is referred to herein, the salts of such acids are also to be included. The preferred polyphosphonic acids of this invention are stable in acidic aqueous solutions. When such acids are referred to as being "stable", it is meant that the acids do not decompose other than to form normal ionic species. It is preferred that the polyphosphonic acid be one that is at least partially soluble in water. By "at least partially soluble", it is meant that such polyphosphonic acid is soluble in water in an amount of at least about 0.1%, by weight. It is more preferred that the acid be water soluble in an amount of at least about 5%, by weight, and most preferred that the acid be miscible in water in ail proportions .

The polyphosphonic acids cf the present invention are phosphonic acids that have two or more anionic phosphonic acid groups on each molecule. Thus, di-, tri-, tetra-, penta-, or other polyphosphonic acids are all to be included herein in the term "polyphosphonic" acids. Other acidic groups, such as carboxylic, boric, and the like, can also be present on the molecule in addition to the phosphonic acid groups. Polymers that have at least two pendent phosphonic acid groups, wherein each such pendent phosphonic acid group is a mono- functional phosphonic acid group, are also included as polyphosphonic acids. Such phosphonated polymers can be of the general formula:

(?oy_z wherein R° is alkylene, arylene, alkylarylene, aminoalkylene, or aminoarylene; wherein x is the number of monomer units in the backbone of the base polymer; and wherein M is hydrogen; an -alkaline metal, such as sodium, potassium and the like; or alkyl, such as methyl, ethyl, propyi, and the like.

Such phosphonated polymers wherein the pendent groups each comprise two or more phosphonic acid groups are also to be included as polyphosphonic acids. More preferred are di-, tri-, tetra-, and penta-phosphonic acids that are polyphosphonic acids having two, three, four or five anionic phosphonic acid groups attached to a non-polymeric central portion. It should be pointed out that mono-functional phosphonic acids, that is, molecules that contain only one anionic phosphonic acid group, are not considered to be "polyphosphonic acids" or "polyphosphonates" , as those terms are used herein. It is preferred that the subject polyphosphonic acids are organic acids and it is more preferred that such polyphosphonic acids are aminoalkylpolyphosphonic acids, or hydroxyalkylpolyphosphonic acids having the general formula: RA(CK₂-(P0₃)M₂)_x or,

RA((PO₃)M₂)_X

where M is hydrogen; an alkaline metal, such as sodium, potassium and the like; or alkyl, such as methyl, ethyl, propyi, and the like; R⁷ is amino, aminoalkyl, or hydroxyalkyl; and x is a number equal to the number of valences of R⁷, provided that x is 2 or higher.

Illustrative of some of the polyphosphonic acids that are suitable for use in the present compositions and coatings are n-octadecylaminobismethylenephosphonic acid, dodecyldiphosphonic acid, ethylidenediaminotetramethylenephosphonic acid, hydroxyethylidenediphosphonic acid, hydroxypropylidenediphosphonic acid, 1-hydroxyethylidene- I, 1-diphosphonic acid, isopropenyldiphosphonic acid, N,N- dipropynoxy methyl amine trimethylphosphonic acid, oxyethylidenediphosphonic acid, 2-carboxyethylphosphonic acid, N, N-bis( ethynoxy-methyl ) amine methyl tri phosphonic acid, nitriletrimethylenephosphonic acid, aminotrimethylene phosphonic acid, diethylenetriaminepentakis ( methylenephosphonic ) acid, animo( trimethylenephosphonic acid ) , nitrilotris ( methylenephosphonic acid ) , ethylenediaminotetra( methylenephosphonic acid), hexamethylenediaminetetra( ethylenephosphonic .acid) , diethylenetriaminepenta( methylenephosphonic acid ) , glycine, N, N-bis( ethylenephosphonic acid ) , bis( hexamethylenetriamine, penta( methylenephosphonic acid) and 2-ethylhexylphosphonic acid.

Polyphosphonic acids that are preferred for use in the subject invention are aminotri( ethylene phosphonic acid), 1-hydroxyethylidene-l, 1-diphosphonic acid, hexamethylenediaminetetra( methylenephosphonic acid) and diethylenetriaminepenta( methylenephosphonic acid).

The polyphosphonic acids of the present invention can be used in the presence of small amounts of impurities, as long as such impurities do not significantly interfere with the ability of the polyphosphonic acid salt of an ICP to protect a metal surface from corrosion. By way of example, when ammonium peroxidisulfate is used as a chemical oxidant for the polymerization of the ICP, some amount of sulfate salt is formed as a by-product of the reaction. The sulfate can also act as a dopant for the ICP and compete with the polyphosphonic acid for dopant sites. However, the sulfate that is present as a dopant from this source does not significantly interfere with the ability of the polyphosphonic acid-doped ICP to protect a metal surface from corrosion. Regular commercial grades of the polyphosphonic acid which are widely available at reasonable cost are suitable for use.

Other components :

Optionally, other components such as pigments, binders, surfactants, plasticizers , other polymers, solvents or dispersion liquids, processing aids and the like can be added to the compositions and coatings of the present invention in order to improve their performance in certain applications. Solvents, which may also be referred to herein as

"dispersion liquids", can be included in the coating composition as carrier liquids for the ICP polyphosphonate and other ingredients . Depending upon the nature of the ingredients, the solvent can be aqueous, non-aqueous, or an aqueous/non-aqueous mixture. It is not necessary that all or any portion of the ICP polyphosphonate be soluble in the solvent and suitable compositions can be prepared by conventional dispersion methods wherein the solids are finely dispersed in the solvent mixture to form a coating composition. If organic solvents are used as solvents, almost any organic material may be used so long as it will permit the formation of a solid coating containing the ICP polyphosphonate. It is preferred that such organic materials be liquids at the temperature at which the coating composition is applied. Illustrative of suitable organic solvents are alcohols, such as ethanol, ethanol, propanol, butanol, and the like; ketones, such as methyl ethyl ketone, acetone, and the like; aromatics, such as xylene, toluene, phenol, benzene, naphthalene, and the like; amides, such as dimethylsulfoxide and dimethylacetamide; ethyl acetate; alkanes, such as hexane and the like; ethers, such as tetrahydrofuran and the like; and mixtures thereof. Preferred solvents are acetone, ethanol, ethyl acetate, hexane, tetrahydrofuran and mixtures of acetone and ethanol, methyl ethyl ketone, n-butanol and mixtures of methyl ethyl ketone and n- butanol .

The subject coating composition and coating can also contain a binder. Any conventional binder material can be used as long as it provides the composition and coating with desirable adhesion and other typical binder properties and does not interfere with the electrical conductivity of the ICP polyphosphonate. Suitable binders can be selected from drying oils, such as linseed oil, soybean oil, safflower oil, talc oil, cottonseed oil, tung oil, and oiticica; ther oset resins,, such as alkyds, epoxies, unsaturated polyesters, thermosetting acrylics, phenolics and polyurethanes ; thermoplastic resins, such as polyesters, polyamides and polycarbonates. Cross-linkable binders particularly suitable for this application include the two-component cross-linkable polyurethane and epoxy systems (See, e.g., U.S. Pat. No. 5,532,025, which is incorporated by reference herein) as well as the polyvinylbutyral system that is cross-linked by the addition of phosphoric acid in butanol.

Polyvinyl butyral resin has been found to be a preferred binder for the present coating compositions. Polyvinyl butyral resins are copolymers of polyvinyl butyral, polyvinyl alcohol and polyvinyl acetate.

Polyvinyl butyral resins having about 80%, by weight, polyvinyl butyral, 0 - 1.5%, by weight, polyvinyl acetate and 18% - 20%, by weight, polyvinyl alcohol have been found to be more preferable. The use of polyvinyl butyral resins (PVB) as components of the present coating compositions has been found to be particularly advantageous because coatings composed solely of ICP's often do not bind tightly enough to steel to prevent some separation of the coating from the steel surface and thereby permit corrosion to occur by penetration of the corrosive environment under and around the coating.

However, the combination of PVB and the ICP salts of the present invention unexpectedly results in a coating that binds very tightly to steel, even when the steel has not been sand-blasted and also provides superior corrosion resistance. This synergistic binding property has been found to result not only in superior corrosion protection in scratches or pinholes that penetrate the coating, but also to minimize the spread of corrosion under the coating away from the scratch cr pinhole. In commercial practice, therefore, such a coating offers a significant benefit in time and expense when it can be applied over a metal surface that has merely been cleaned, rather than sand-blasted.

Preparation of ICP and ICP polyphosphonate:

ICP monomers are polymerized into ICP's to form a component of the subject compositions and coatings. As used herein, the terms "coating composition" and "composition" is meant to include the ICP polyphosphonate when it is present as a dispersion, emulsion or solution in liquid form in a solvent or dispersion liquid. Such coating composition can comprise only the ICP polyphosphonate in such liquids, or can include any and all of the other components discussed above. The composition can be applied to a metal surface to be protected, but upon removal of some or all of the solvent or dispersion liquid, such as by drying, the composition becomes a solid "coating", as that term is used herein. An "electrically conductive corrosion resistant coating composition", is intended to mean that a pellet pressed from a dry powder of such composition is electrically conductive. As used herein, the term "electrically conductive" means having a conductivity of at least about 10"⁸ S/cm.

As previously mentioned, the ICP can be a polyunsaturated homopolymer or copolymer having a polyconjugated rt electron system along the polymer backbone and being electrically conductive in at least one valence state. Such ICP's are well known in the art and a comprehensive summary of ICP technology can be found in Synthetic Metals , vols . 17 - 19, 1987; vois. 28 - 30, 1989; and vols. 40 - 42, 1991, incorporated by reference herein.

Illustrative of ICP's useful in the subject coating are poly( unsaturated ) polymers such as substituted and unsubstituted pol ( heteroaromatics ) , such as polythiophenes, poly( furans ) , polypyrroies, polyquinolines , polyisothianaphthenεs , polycarbazoles , poly(alkyl thiophenes) and the like; substituted cr unsubstituted poly( aromatics ) such as polyphenylene sulfides, polyanilines, polyphenylenes, polvnaphthalenes and polyperinaphthalenes , poly( azulenes ) ; and substituted or unsubstituted poly( aromatic vinylenes ) , such as poly( phenylene vinylene ) , poly( dimethoxy phenylene vinylene ) , poly( naphthalene vinylene) and the like; and substituted or unsubstituted poly( heteroaromatic vinylenes) such as poly( thienylene vinylene), poly( furylene vinylene), poly( carbazole vinylene), poly(pyrrole vinylene) and the like; and copolymers thereof. Preferred ICP homopolymer or copolymers are substituted or unsubstituted poly( heterocyclics ) , poly( anilines ) and aromatic or heteroaromatic vinylenes. More preferred ICP's are polyanilines. The most preferred ICP is unsubstituted polyaniline.

The ICP polyphosphonate can be synthesized by any of several methods. ICP monomers can be polymerized into an ICP in the presence of a polyphosphonic acid to yield an ICP polyphosphonate and the polymerization can be carried out in the presence of either a chemical oxidant or an electrochemical potential. Alternatively, the ICP polyphosphonate can.be formed by contacting a polyphosphonic acid with the base form of the ICP. For example, polyphosphonic acid-doped polyaniline can be produced by contacting the emeraldine base form of polyaniline with a polyphosphonic acid that re-dopes the polymer and forms the polyaniline polyphosphonate salt. This method of ICP salt formation has been discussed by Chiang and MacDiarmid, Synzh . Metals , 13 : 193 , 1986; MacDiarmid et al . , Synth . Metals , 18 : 285 , 1987; and MacDiarmid and Epstein, Faraday Discuss . Chem . Soc , 88 : 311 , 1989; each of which is incorporated by reference herein. Other methods can also be used to form the ICP polyphosphonate. A polyphosphonic acid can be contacted with an ICP salt of a mineral acid such as hydrochloric or sulfuric, or even another organic acid, and a dopant exchange can take place with the result that the ICP polyphosphonate is formed.

In one embodiment of the present invention, the ICP polyphosphonate is produced by the polymerization of an ICP monomer in the presence of a polyphosphonic acid. This method of synthesis is well known in the art and is discussed in general by MacDiarmid, The polyanilines : a novel class of conducting polymers , Chap. 6 in Conjugated Polymers and Related Materials, Ed's. Salaneck, Lundstrom and Ranby, Oxford U. Press, Oxford, 1993; and Genies et al., Synth. Metals , 36 : 139 - 182, 1990. The polymerization of the ICP monomers is facilitated by the presence of an oxidant, which can be either a chemical oxidant, such as ammonium peroxidisulfate, FeCl₃, FeCl₃- plus-peroxide, and the like, or can be an oxidizing electrical potential .

Methods for the chemical oxidative polymerization of ICP's such as polyaniline and polypyrrole has been discussed in detail in U.S. Pat. No's. 4,567,250, 4,731,408, 4,940,517, 4,983,322, 5,006,278 and 5,567,356, and by Li, et al . , Synth . Metals , 20:141 - 149, 1987, each of which is incorporated by reference herein. Likewise, methods for the electrochemical polymerization of ICP's have been discussed by Genies et al . , id. ; Lukkari, Mat. Sci . Forum , 191 : 219 - 224, 1995; Skaakrup eϋ al . , Mat. Res . Soc Symp . Proc , 369 : 565 - 574, 1995; Rajapakse and Lankeshwar , J. Natn . Sci . Coun . Sri Lanka , 22(3) :291 - 299, 1994; Pokhodenko and Krylov, Synth. Metals , 41 - 43 : 533 - 536, 1991; and Lapkowski, Synth. Metals , 55 - 57:1558 - 1563, 1993; and in U.S. Pat. No. 4,615,829. Electrochemical polymerization of organic soluble ICP's is also described in co-pending U.S. Pat. Application Serial No. 08/868,094, which is incorporated by reference herein.

A preferred method for the synthesis of the ICP polyphosphonate that is used in one embodiment of the present invention is by chemical oxidative polymerization of the ICP monomer in the presence of a preferred polyphosphonic acid in the polymerization medium. In brief, the ICP monomer and the polyphosphonic acid are added to a reaction solvent, which can be either aqueous, non-aqueous, or an aqueous/non-aqueous liquid mixture. The ICP monomer, polyphosphonic acid, reaction solvent mixture is then chilled to between 0°C and 20 °C and a chemical oxidant, commonly in a mixture with the same solvent that is used for the reaction solvent, is slowly added to the reaction mixture over a period of time, such as from 15 minutes to over one hour, with vigorous agitation of the reaction mixture. After all reactants have been added to the reaction mixture, the mixture is stirred at a reduced temperature for several hours, such as from 4 hours to 24 hours.

The amounts of the reactants named in the method given above can vary widely. It is preferred that the ICP monomer be present in the reaction mixture in a molar concentration of from about 0.05 molar to about 20 molar, more preferably from about 0.1 molar to about 10 molar and most preferably, from about 0.5 molar to about 5 molar. The amount of the polyphosphonic acid present in the reaction mixture is based upon the amount of ICP monomer and is preferably from about 0.1 to about 2.0 moles polyphosphonic functional anionic acid group per mole of ICP monomer, more preferably from about 0.2 to about 1.0 moles polyphosphonic acid group per mole of ICP monomer and most preferably from about 0.4 to about 0.6 moles polyphosphonic acid group per mole of ICP monomer. If a chemical oxidant, such as ammonium percxidisulfate is used to facilitate the polymerization of the ICP monomer into an ICP, such oxidant is preferably present in an amount of from about 0.1 to about 3 moles per mole of ICP monomer, more preferably in an amount of from about 0.5 to about 2 moles per mole of ICP monomer and most preferably in an amount of from about 0.8 to about 1.4 moles per mole of ICP monomer.

After the completion of the polymerization, the ICP polyphosphonate may precipitate spontaneously, or may be precipitated by the addition of a suitable precipitant (such as acetone if the reaction medium is aqueous) and the precipitated ICP polyphosphonate recovered by filtration and washed with water and/or a polar organic solvent to remove any unreacted ICP monomers or oxidant and unwanted by-products. If the ICP polyphosphonate is produced by an aqueous/organic emulsion polymerization method, the organic phase that contains the ICP polyphosphonate can be separated from the aqueous phase and used as is or dissolved into another organic carrier solvent such as xylene.

At this point, the ICP polyphosphonate is electrically conductive and a pellet pressed from such material will exhibit an electrical conductivity of at least about 10^"8 S/cm. The ICP polyphosphonate can be in either solid form or in a mixture with a solvent and is ready to be incorporated into a coating composition.

Preparation of the coating composition and the coating:

The subject coating composition can be simply the ICP polyphosphonate mixed with a suitable solvent. The mixture can be a dispersion, an emulsion or a true solution. However, in order to impart desirable properties to the coating that results from the composition, such as adherence, color, durability and the like, it is common to add other materials as described above to the ICP polyphosphonate and solvent mixture. Such other materials can be added at any time during the formation of the coating composition, so long as their presence does not cause unwanted reactions or interferes with reactions that are desired. For example, some of the pigments and other polymeric materials could be present during the ICP polymerization reaction, or could be added to the ICP polyphosphonate at any time after such polymerization.

One embodiment of the subject coating composition is formed by mixing together the desired amounts of the ICP polyphosphonate, solvent, binder and any other desired materials. Such mixing can take place in a ball mill, a kneader-type mixer, an extruder, a roller mill, a pin mill, a pug mill, or any other mixer that provides high shear and that can handle viscous liquids . By way of example, the materials can be suitably mixed into a coating composition by placing all ingredients in a ball mill and milling at room temperature for 10 hours. In the preparation of an embodiment of the subject coating composition that comprises materials other than the solvent and the ICP polyphosphonate, the components are blended in a ratio that maintains the property of the binder to adhere to a metal surface while also maintaining the conductivity property of the ICP polyphosphonate so that it is capable of providing corrosion resistant properties. The amount of the ICP polyphosphonate included in the coating composition may vary widely, and any amount which improved the anti- corrosive properties to any extent may be used. The ICP polyphosphonate is employed in the coating composition in at least an anti-corrosive amount. Preferably, the ICP polyphosphonate is present in the coating composition in an amount of from about 0.01% to about 50% wt/wt, more preferably in an amount of from about 0.05% to about 30%, even more preferably in an about of from about 0.1% to about 25% and most preferably in an amount of from about 0.5% to about 10% wt/wt. The balance of the coating composition includes the solvent and any other additives and ingredients that are desired.

When the ICP polyphosphonate is present in the coating composition at these levels, the content of the ICP polyphosphonate in the resultant coating can be from about 2% to 25%, by weight, preferably from about 4% to 20% and more preferably about 5% to 15%. The conductivity of such coating is at least about 10^"8 S/cm, and is preferably at least about 10^"6 S/cm. In other embodiments of the invention, however, it may be desirable that ICP polyphosphonates be present in the coating at a concentration of 30%, by weight, or even higher.

Applications of the coating composition and the coating: The coating composition of the present invention can be applied to the surface of an corrodible metal for the purpose of forming an anti-corrosion coating on the surface of the metal. The metal surface or object to be coated can be virtually any metal that is subject to corrosion. Thus, virtually all metals and metal alloys can be used in conjunction with the present invention including silver, aluminum, iron, nickel, copper, zinc, cobalt, lead, iron-based alloys such as steel, tantalum, titanium, zirconium, niobium, chromium, and the like, and alloys thereof. The surface of the corrodible metal that is to be protected can be cleaned prior to^{" "}application of the coating composition if it is desirable to improve the adhesion of the coating. The metal surface can be cleaned chemically, such as by inhibited acids, or physically, such as by sanding, scraping, sand blasting, or other methods known in the art for forming a bare "white" metal surface. An advantage of an embodiment of the present coating composition that includes PVB, however, is that it adheres tightly to a metal surface that has merely been cleaned, but not sand-blasted.

The subject coating compositions can be applied to the metal surface to form coatings by conventional procedures. For example, compositions may be applied by brush and rollers, air or airless spray equipment, electrostatic, hot, or steam spaying; use of aerosol packaging; dip, flow and electrodeposition coating; roller coating machines; and powder coating. After the coating composition is applied, a coating is formed by the removal of all or part of any solvents or dispersion liquids that were components of the composition, and a solid, cohesive coating is formed over the surface of the metal to form a protected metal surface. As used herein, the term "protected metal surface" is to be understood to mean a surface of a corrodible metal on which a coating has been formed from the coating composition of the present invention. The purpose of the subject coating is to prevent or minimize corrosion. As mentioned previously, the presence of the ICP polyphosphonate is believed to passivate the metal surface. Although the inventors do not wish to be bound by this or any other particular theory, it is believed that one reason^" that polyphosphonic acid doped ICP's are excellent anti- corrosion materials for iron or steel is that the doped and conductive ICP salt causes the surface potential of the coated metal to shift into the passive regime

(anodizes the surface), and be maintained in this passive state, combined with the ability of the polyphosphonic acid dopant to readily form a complex with the positively charged metal surface, thereby forming a stable passive layer and protecting the surface from corrosion. This combination of properties seems to provide the ICP polyphosphonate with improved corrosion protection of scratches and pinholes that penetrate the coating compared to a coating that contains an ICP sulfonate or an ICP monophosphonate. When the subject ICP polyphosphonate-containing coating is used to .coat steel, for example, it demonstrates the surprising property of causing the galvanic polarity of the steel underlying pinholes and scratches in the coating to move toward neutrality over time, thereby lessening the tendency of the metal to corrode. In contrast, coatings containing ICP sulfonates apparently do not demonstrate such property.

The coating of the present invention is formed from the coating composition as described previously. The coating may be of any thickness that provides anti- corrosion protection fcr the metal surface. However, it is preferred that the coating be at least about 0.1 mil in thickness, more preferably at least about 0.8 mil in thickness, and most preferably at least about 1.5 mil in thickness . The coating compositions and coatings of this invention are useful for such purposes for which conventional paints and coatings are used. For example, these coating compositions can be applied as topcoats, fillers, primers, surfacers and sealers. They can also be used as undercoats and interlayers^" between a metal and a non-metal or between two metal layers. When a coating of the present invention is applied as an undercoat to a sufficiently thin metal film, it has the ability to protect the opposite side of the metal film from corrosion.

The following examples describe preferred embodiments of the inventions. Other embodiments within the scope of the claims herein will be apparent to one skilled in the art from consideration of the specification or practice of the invention as disclosed herein. It is intended that the specification, together with the examples, be considered exemplary only, with the scope and spirit of the invention being indicated by the claims which follow the examples .

REFERENCE EXAMPLE 1 This example illustrates the synthesis of the polyaniline salt of aminotri( methylene phosphonic acid) (PANI-ATMP).

Aminotri( methylene phosphonic acid), (29.9g, 0.1 moles, Dequest® 2000, ( ATMP ) available from Solutia Inc., St. Louis, Missouri) and water (200 ml) were added to a stirred and temperature controlled reaction vessel and chilled to 0°C after which aniline (17 ml, 0.2 moles) was added. Ammonium peroxydisulfate (54.43 g, 0.24 moles, in 120 ml water) was added dropwise over 14 minutes. After stirring for 5.5 hours, a dark green solid precipitate formed in the reaction mixture. Acetone (1.0 liter) was added to the reaction mixture to precipitate the product and the precipitate was recovered by vacuum filtration. The precipitate was washed successively with 4 x 100 ml aliquots of 0.5% DQ2000 in water, 6 x 100 ml aliquots of methanol and 6 x 100 ml aliquots of ether. After drying in air, 22.68 g of product in powder form was recovered. A portion of the powder (5 g) was compressed into a pellet (8000 psig for 5 minutes) arid its electrical conductivity was measured by the four probe method described in "Laboratory Notes On Electrical And Galvanometric Measurements", by H. H. Wieder, Elsevier Scientific Publishing Co., New York, 1979, and was found to be 8.54 S/cm.

The weight average molecular weight, l ., of the polyaniline salt of aminotri( methylene phosphonic acid (PANI-ATMP) was measured by gel permeation chromatography (GPC) using a refractive index detector. For the procedure, two Ultrastyragel columns with diameters of 10⁵ Angstroms and 10^J Angstroms were used at a flow rate of 0.5 ml/min and at a controlled temperature of 45 °C. N- methyl pyrrolidone ( MP ) solution containing 0.1% ammonium formate was used as GPC eluent or solvent. The polyaniline polymers were treated with ammonium formate to convert the polyaniline to its acid form and the molecular weight of the polymer was measured by GPC. The GPC columns were calibrated by twelve polystyrene standards with molecular weights ranging from l.lxlO⁶ to 3000 g/mole. The weight average molecular weight, M„, of the PANI-ATMP was found to be 17,800.

The thermal stability of the material was found to be 210 °C as measured by thermal gravimetric analysis (TGA). The TGA analysis was carried out on a Perkin- Elmer TGS-2 thermogravimetric analyzer with software supplied by Instrument Specialists. The criterion for thermal stability was the onset temperature of the first major weight loss step above 100 °C. A 3 mg sample was used and the analysis was carried out in a dry nitrogen atmosphere with a heating rate of 10°C/min. The same synthesis was repeated, but with approximately a 3-fold scale-up of materials; i.e., 186.45 g of DQ2000 and 51 ml of aniline in 600 ml water; 167.99 g of ammonium peroxidisulfate in 300 ml water was added dropwise and the precipitation and washing was carried out as above except at 3x scale. The product recovered (59.49 g) had a conductivity of 4.48 S/cm as measured on a pellet of the material, and had a molecular weight by GPC of 16 400.

REFERENCE EXAMPLE 2

This illustrates the synthesis of the polyaniline salt of 1-hydroxyethylidene-l, 1-diphosphonic acid (PANI- HEDA ) . To a stirred and temperature controlled reaction vessel was added 1-hydroxyethylidene-l, 1-diphosphonic acid (34.74 g, 0.1 mole, Dequest® 2010, available from Solutia Inc.), and 200 ml water. After the mixture was chilled to 0°C, aniline (17 ml., 0.2 moles) was added and a white emulsion was formed. The temperature was increased to 5°C as ammonium peroxidsulfate (56.12 g, 0.25 moles, in 120 ml water) was added dropwise. After stirring the mixture for about 14 hours a dark green suspension formed. Acetone (1 liter) was added to the reaction mixture to precipitate the product, which was recovered by vacuum filtration and washed successively with 4 x 150 ml aliquots of acetone, 3 x 150 ml aliquots of isopropanol and 3 x 150 ml aliquots of ether. 59.84 g of PANI-HEDA product was recovered. A portion of the powder (5.2 g) was compressed into a pellet (8,000 psig for 5 min. ) and its conductivity was measured by the four-probe method and found to be 1.8 S/cm. The weight average molecular weight was found to be 24,700 by the GPC method described in Reference Example 1. The thermal stability of the material was 227 ^βC as measured by TGA. EXAMPLE 1 This illustrates the preparation of coating compositions containing the polyaniline salt of aminotri( methylene phosphonic acid) (PANI-ATMP) or the polyaniline salt of 1-hydroxyethylidene-l, 1-diphosphonic acid (PANI-HEDA) in suitable solvents with and without phosphoric acid.

The components that were used in the coating compositions are listed in Table 1 by weight and by weight percent of the coating composition. All components except for phosphoric acid, water and polyaniline phosphonate were added to a glass jar. The polyvinyl butyral resin is type B-90, available from Solutia Inc., St. Louis, Missouri. The mixture was stirred and placed in an ultrasonic bath to facilitate dissolution. After the solids dissolved, phosphoric acid (if called for) in water solution was added to the viscous solution. After mixing thoroughly, the solution was transferred to a ball mill, the polyaniline phosphonate was added and the mixture was milled for 14 hours. Upon removal from the ball mill, the coating composition was ready for application.

TABLE 1 : COMPONENTS OF COATING COMPOSITIONS CONTAINING POLYANILINE SALTS OF PHOSPHONIC ACIDS (in igrams and weight percent)

I o

EXAMPLE 2 This illustrates the preparation of coating compositions containing polyaniline salts of several phosphonic and sulfonic acids. Initially, a polymer solution was prepared by adding polyvinyl butyral resin (111 g., PB-90, Butvar® B- 90, available from Solutia Inc., methyl ethyl ketone (444 g), and n-butanol (363 g), to a 1 gallon glass jar with stirring and the jar was placed in an ultrasonic bath. When the mixture became a yellowish viscous solution and when all of the PB-90 had dissolved, a solution of phosphoric acid (0.72 g. of 85% phosphoric acid) in deionized water (6.48 g) was added with further stirring until well mixed. This polymer solution, which contained no polyaniline salt, was used as the control in the salt- fog test of corrosion resistance.

Various polyaniline salts were added to the polymer solution described above to prepare the coating compositions to be tested. Each of the test compositions was formulated to contain about 2%, by weight, of the polyaniline salt. To form coating composition I, Versicon® (2.51g, available from Monsanto Co.) was added to 120 g of the polymer solution. Versicon® is a proprietary polyaniline that is doped with more than one sulfonic acid. Coating composition II ( PANI-DNNDSA) was prepared in a similar manner as I, by adding polyaniline doped with dinonylnaphthalenedisulfonic acid (2.67 g) to the polymer solution (100 g). Coating composition III was prepared by adding PANI-ATMP prepared as described in Reference Example 1 (3.92 g) to the polymer solution (200 g). Coating composition IV (PANI-PSSA) was prepared by adding polyaniline salt of polystyrenesulfonic acid (2.5 g) to the polymer solution (100 g). Coating composition V (PANI-ME(P0₃H₂) was prepared by adding the polyaniline salt of methyl phosphonic acid (1.64 g) to the polymer solution (100 g). After mixing the polymer solution with the polyaniline salt, all coating compositions were placed in a ball mill with 1/2" ceramic grinding media and subjected to milling overnight. The coating compositions were then ready for application.

EXAMPLE 3 This illustrates the ability of the coating compositions prepared in Example 2 to protect steel from corrosion in a salt-fog test. Steel "Q" panels (3" x 6") were washed with acetone and air dried. The panels were not sand-blasted. Five panels were used for each of the five coating compositions and for the control . A total of 30 panels were prepared. To each of five panels, a 30 mil thick wet coat of one of the coating compositions described in Example 2 was applied to one side of the panel and allowed to dry overnight. The thickness of the wet films of the coating compositions and the control were 30 mil. The panels were allowed to dry overnight. After drying the film thickness of the dry films was measured at eight locations on each panel and an average dry film thickness was calculated for each panel. The average dry film thickness for each of the five replicate panels were then averaged to arrive at an overall average dry film thickness for each coating composition and the control. Such average dry film thicknesses were found to be 1.26 mil for composition I; 1.78 mil for composition II; 1.32 mil for composition III; 1.84 mil for composition IV; 1.76 mil for composition V; and 0.8 mil for the control. After the coatings were dry, a topcoat of Carboline 890® was applied to a wet film thickness of 10 mil. Each of the panels was also coated on the backside to protect from corrosion and the panels were then allowed to dry again. After drying, the side of each panel having the test coating or control was scribed with a carbide scriber tool in the shape of an "X" that was centered on the panel and extended roughly three-quarters of the length of the panel. The scribed mark penetrated both the primer coating and the topcoat and exposed bare metal. The edges of each panel were then covered with protective tape to prevent any corrosion of the edges of the panel .

All panels were then placed in a salt-fog test chamber and exposed to standard salt-fog exposure regimine for a total of 1500 hours. The panels were removed at 166, 334, 502, 1000, 1332 and 1500 hours and the degree of corrosion along the scribed mark was measured as described below and a "corrosion score" was assigned to each panel.

The salt-fog "corrosion score" is an arbitrary scale designed to provide a quantitative rating for the degree of corrosion of coated steel sample panels that have been prepared as described above. The rating scale was defined by the preparation and exposure of a number of samples of coated and scribed steel panels. After exposure to the salt spray, 10 panels that had different degrees of corrosion, ranging from substantially none to extensive corrosion and weeping, were selected and photographed along with a panel having no salt spray exposure. Depending upon the extent of corrosion, each panel was assigned a number from 0 (no corrosion by visual inspection) to 10 (extensive corrosion within the entire scribed area). An unknown sample is rated by comparing its appearance with the photographs of the rated standards and identifying the standard sample which compares most closely with it. The unknown is then given a "corrosion score" that is equal to the rating number of that standard.

Five replicate panels coated with one of the five test coatings or the PVB standard coating were placed in the test chamber and exposed to salt spray. At the end of 166 hrs., 334 hrs . , 502 hrs . , 1000 hrs . , 1332 hrs . and 1500 hrs., each one of the 30 panels was removed from the test chamber and rated for corrosion as described above. The raw scores from each of the five replicate panels for each coating were used to calculate a mean score for each coating at each of the time periods. Table 2 shows the mean corrosion scores for each of the coating compositions at each time of exposure.

0) TABLE 2: CORROSION SCORE AT SCRIBE LINES FOR COATINGS CONTAINING POLYANILINE SALTS

C CO cn

H

H m x rn UJ

LΠ

3)

C r m ι

O)

The mean corrosion score for each coating was plotted versus the time of exposure in the salt-fog chamber and that data is shown in Figure 1. As described above, the "corrosion score" is inverse to the degree of protection provided by a coating. In other words, lower scores indicate better corrosion protection than higher scores. In Figure 1, it is seen that the coating containing the PANI-ATMP has the best performance of any of the coatings tested. Until the 1332 hour period, the PANI-ATMP coating is clearly superior to all other coatings. After 1000 hours, the scores of several of the coatings appear to improve. However, it is felt that this may reflect an artifact of the testing and scoring method, since it is doubtful that the corrosion on any of the panels actually improved with time. Thus, if the performance of the coatings through the first 1000 hours is given more weight than results after 1000 hours, the superiority of the PANI-ATMP coating is even clearer. After all panels were removed from the test chamber after 1500 hours and scored for scribe corrosion as described above, they were soaked in methylene chloride and the coatings were removed. The panels were then graded for the spread cf corrosion of the metal surface under the coatings on either side of the scribed line by measuring the width (in mm) of the corroded area normal to the scribe lines at four positions on each of the four legs of the "X" . These measurements are used to calculate the average corrosion spread (mm) for each of the four legs of the "X" of each panel and from these measurements a mean value is calculated for the corrosion spread for each coating. Such mean values of corrosion spread after 1500 hrs. were: 5.41 for composition I; 5.57 for composition II; 2.25 for composition III; 4.21 for composition IV; 2.61 for composition IV; and 9.55 for the control. Since the corrosion spread is a measure of the width (in mm) of spread of the corroded area away from the scribed lines, a lower number means less corrosion spread and, thus, better corrosion protection. The corrosion spread data was plotted for each coating composition and the control in Figure 2. Again, the superiority of the PANI-ATMP containing coating is evident. Although the coating containing polyaniline doped with methylphosphonic acid ( PANI-ME( P0₃H₂ ) ) demonstrated better resistance to corrosion spread than all coatings other than that containing PANI-ATMP, it was still second, to the PANI-ATMP coating and did not perform particularly well in the scribe corrosion test described above .

Based on the results for scribe corrosion and corrosion spread, it is concluded, therefore, that the coating containing polyaniline doped with a polyphosphonic acid was superior to coatings containing polyanilines doped with sulfonic acids and monophosphonic acid.

In view of the above, it will be seen that the several advantages of the invention are achieved and other advantageous results obtained.

As various changes could be made in the above methods and compositions without departing from the scope of the invention, it is intended that all matter contained in the above description and drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

What is claimed is:

1. An electrically conductive corrosion resistant coating composition comprising an intrinsically conductive polymer salt of a polyphosphonic acid.

2. A coating composition as set forth in claim 1, wherein said polyphosphonic acid is an organic polyphosphonic acid.

3. A. coating composition as set forth in claim 2, wherein said polyphosphonic acid is an organic di-, tri-, tetra- or penta-phosphonic acid.

4. A coating composition as set forth in claim 3, wherein said polyphosphonic acid is an aminoalkylpolyphosphonic acid, or a hydroxyalkylpolyphosphonic acid.

5. A coating composition as set forth in claim 3, wherein said polyphosphonic acid is n- octadecylaminobismethylenephosphonic acid, dodecyldiphosphonic acid, ethylidenediaminotetramethylenephosphonic acid, hydroxyethylidenediphosphonic acid , hydroxypropylidenediphosphonic acid, 1-hydroxyethylidene- 1, 1-diphosphonic acid, isopropenyldiphosphonic acid, N,N- dipropynoxy methyl amine trimethylphosphonic acid, oxyethylidenediphosphonic acid, 2-carboxyethylphosphonic acid, N, N-bis( ethynoxy-methyl ) amine methyl tri phosphonic acid, nitriletrimethylenephosphonic acid, aminotrimethylene phosphonic acid, diethylenetriaminepentakis ( methylenephosphonic ) acid , animo( trimethylenephosphonic acid), nitrilotris(methylenephosphonic acid ) , ethylenediaminotetra( methylenephosphonic acid ) , hexamethylenediaminetetra( methylenephosphonic acid ) , diethylenetriaminepenta( methylenephosphonic acid ) , glycine,N, N-bis( methylenephosphonic acid) , bis( hexamethylenetriamine, penta( methylenephosphonic aci ) or 2-ethylhexylphosphonic acid.

6. A coating composition as set forth in claim 5, wherein said polyphosphonic acid is aminotri( methylene phosphonic acid), 1-hydroxyethylidene-l, 1-diphosphonic acid, hexamethylenediaminetetra ( methylenephosphonic acid), or diethylenetriaminepenta( methylenephosphonic acid) .

7. A coating composition as set forth in claim 5, wherein said intrinsically conductive polymer is a substituted or unsubstituted polyaniline, polypyrrole, or polythiophene .

8. A coating composition as set forth in claim 5, wherein said intrinsically conductive polymer is an unsubstituted polyaniline.

9. A coating composition as set forth in claim 6, wherein said intrinsically conductive polymer is an unsubstituted polyaniline.

10. A coating composition as set forth in claim 9, wherein said intrinsically conductive polymer is the polyaniline salt of aminotri( methylene phosphonic acid).

11. A coating composition as set forth in claim 9, wherein said intrinsically conductive polymer is the polyaniline salt of 1-hydroxyethylidene-l , 1-diphosphonic acid) .

12. A coating composition as set forth in claim 1, wherein said coating further comprises one or more polymer, binders pigment, surfactant, plasticizer, or anti-oxidants .

13. A coating composition as set forth in claim 12, wherein said coating further comprises water, methanol, ethanol, an amide, ethyl acetate, an alkane, an ether, propanol, butanol, methyl ethyl ketone, acetone, xylene, toluene, phenol, benzene, naphthalene, or a mixture thereof.

14. A coating composition as set forth in claim 3, wherein said coating further comprises polyvinyl butyral resin.

15. A coating composition as set forth in claim 6, wherein said coating further comprises polyvinylbutyral resin.

16. A coating composition as set forth in claim 6, wherein said intrinsically conductive polymer salt of a polyphosphonic acid is present in the coating composition in an amount of from about 0.1% to about 25%.

17. A coating composition as set forth in claim 16, wherein said intrinsically conductive polymer salt of a polyphosphonic acid is present in the coating composition in an amount of from about 0.5% to about 10% wt/wt.

18. A method for producing a corrosion resistant coating composition for a corrodible metal comprising mixing an intrinsically conductive polymer salt of a polyphosphonic acid and a solvent.

19. A method for producing a corrosion resistant coating composition as set forth in claim 18, wherein said polyphosphonic acid is an organic di-, tri-, tetra-, or penta-phosphonic acid.

20. A method for producing a corrosion resistant coating composition as set forth in claim 18, wherein said polyphosphonic acid is an aminoalkylpolyphosphonic acids, or a hydroxyalkylpolyphosphonic acid.

21. A method for producing a corrosion resistant coating composition as set forth in claim 19, wherein said polyphosphonic acid is n- octadecylaminobismethylenephosphonic acid , dodecyldiphosphonic acid, ethylidenediaminotetramethylenephosphonic acid, hydroxyethylidenediphosphonic acid, hydroxypropylidenediphosphonic acid, 1-hydroxyethylidene- 1, 1-diphosphonic acid, isopropenyldiphosphonic acid, N,N- dipropynoxy methyl amine trimethylphosphonic acid, oxyethylidenediphosphonic acid, 2-carboxyethylphosphonic acid, N,N-bis( ethynoxy-methyl ) amine methyl tri phosphonic acid, nitriletrimethylenephosphonic acid, aminotrimethylene phosphonic acid, diethylenetriaminepentakis ( methylenephosphonic ) acid, animo( trimethylenephosphonic acid ) , nitrilotris( methylenephosphonic acid ) , ethylenediaminotetra( methylenephosphonic acid ) , hexamethylenediaminetetra( methylenephosphonic acid ) , diethylenetriaminepenta( methylenephosphonic acid), glycine,N,N-bis( methylenephosphonic acid) , bis ( hexamethylenetriamine, penta( methylenephosphonic acid ) or 2-ethylhexylphosphonic acid.

22. A method for producing a corrosion resistant coating composition as set forth in claim 21, wherein said polyphosphonic acid is aminotri( methylene phosphonic acid), 1-hydroxyethylidene-l, 1-diphosphonic acid, hexamethylenediaminetetra(methylenephosphonic acid), or diethylenetriaminepenta( methylenephosphonic acid) .

23. A method for producing a corrosion resistant coating composition as set forth in claim 21, wherein said intrinsically conductive polymer is a substituted or unsubstituted polyaniline, polypyrrole, or polythiophene .

24. A method for producing a corrosion resistant coating composition as set forth in claim 21, wherein said intrinsically conductive polymer is an unsubstituted polyaniline.

25. A method for producing a corrosion resistant coating composition as set forth in claim 22, wherein said intrinsically conductive polymer is an unsubstituted polyaniline.

26. A method for producing a corrosion resistant coating composition as set forth in claim 25, wherein said intrinsically conductive polymer salt of a polyphosphonic acid is the polyaniline salt of aminotri( methylene phosphonic acid), or of 1- hydroxyethylidene-1 , 1-diphosphonic acid ) .

27. A method for producing a corrosion resistant coating composition as set forth in claim 18, wherein said intrinsically conductive polymer salt of a polyphosphonic acid and said solvent is further mixed with one or more polymer, binder, pigment, surfactant, plasticizer, or anti-oxidant .

28. A method for producing a corrosion resistant coating composition as set forth in claim 27, wherein said solvent is selected from water, methanol, ethanol, propanol, butanol, methyl ethyl ketone, acetone, xylene, toluene, phenol, benzene, naphthalene, or a mixture thereof .

29. A method for producing a corrosion resistant coating composition as set forth in claim 27, wherein said coating further comprises polyvinyl butyral resin.

30. A method for protecting a corrodible metal surface from corrosion, comprising applying to the corrodible metal surface a coating composition comprising a solvent and an anti-corrosion effective amount of an intrinsically conductive polymer salt of an organic polyphosphonic acid and causing a solid coating to form which coating substantially covers such corrodible metal surface.

31. A method as set forth in claim 30 wherein said coating composition also contains a polvvinylbutyral resin.

32. A coating for protecting a corrodible metal surface from corrosion comprising an anti-corrosion effective amount of an intrinsically conductive polymer salt of a polyphosphonic acid.

33. A coating as set forth in claim 32, wherein said coating also contains a polvvinylbutyral resin.

34. A coating as set forth in claim 32, wherein said coating has an electrical conductivity of at least about 10^"8 S/cm.

35. A coating as set forth in claim 33, wherein said coating has an electrical conductivity of at least about 10"⁶ S/cm.