Chapter 32
Polyaniline in Corrision-Resistant Coatings
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T. Page McAndrew , Susan A. Miller , Andrew G. Gilicinski , and 2,4
Lloyd M. Robeson
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Polymer Chemicals Technology, Corporate Science and Technology Center, and
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During the past two decades, one of the most active fields of solid -state science has been that of electrically conductive polymers. Electrically conductive polymers are polymers which, though insulators as prepared, can be converted to polymers having many or all of the properties of a metal through appropriate chemical/electrochemical oxidation or reduction. Typical applications considered for electrically conductive polymers have been in areas such as rechargeable batteries and electrochromic devices. Recently it has been reported that polyaniline, in its electrically conductive, protonated form, displays excellent performance as a coating for preventing the corrosion of carbon steel. The present research has shown that in fact, the non-conductive, unprotonated form of polyaniline displays even better performance in corrosion prevention than the conductive form. Moreover, it has been shown that polyaniline can be blended with other polymers (e.g., polyimides) to improve their corrosion resistance performance, or used as a hardener for epoxides or diisocyanates to give very good corrosion resistant coatings. Polyaniline performance is discussed in terms of its ability to form dense, adherent films, and create a basic surface on carbon steel. Electrically Conductive Polymers. During the past two decades, one of the most activefieldsof solid-state science has been that of electrically conductive polymers. Electrically conductive polymers (ECP's) may be generally characterized as polymers that, though insulators as prepared, can be converted to polymers having many or all of the properties of a metal through appropriate chemical/electrochemical oxidation or reduction (processes usually referred to as doping). For example, with the prototype ECP, polyacetylene [(CH) ], oxidative doping with \j vapor raises electrical conductivity (σ)fromca. 10" Q^cm" to ca. 200 Q^cm" - a changefromthe insulating regime to the metallic regime (1-3). For the present discussion, ECP's are X
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Corresponding author.
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©1998 American Chemical Society
In Organic Coatings for Corrosion Control; Bierwagen, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.
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distinguished from extrinsic electrically conductive polymers — insulating polymers in which metallic properties are produced by inclusion of metal fillers (e.g., Ag-filled epoxy or graphite-filled polyethylene). Electrically Conductive Polymers in Coatings. The major applications investigated for ECP's have been typically in areas such as rechargeable batteries, electrochromic devices and charge dissipative coatings ~ applications that take advantage of the high electrical conductivity of ECP's and their ability to undergo facile oxidation/reduction (1-3). One potential use of ECP's, that recently has received considerable attention is in corrosion resistant coatings. Notable among research in this area has been that by a joint groupfromthe National Aeronautics and Space Administration (NASA, Kennedy Space Center, FL) and the Los Alamos (NM) National Laboratory (LANL). It describes the use of the protonated, conductive, emeraldine form of polyaniline (PAn) as a coating for the protection of carbon steel from corrosion (4-8). See Figure 1. It is noted that reports discussing the use of ECP's in corrosion resistant coatings date to 1981(9-75). However, the cited NASA/LANL report was the first to categorically claim utility in the protection of carbon steel. Subsequent to these reports, other reports have been issued regarding the utility of PAn in corrosion resistant coatings (16-24).
N-H J 0.5
0.5 _10
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σ = 10 Q- cm-
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Undoping (OH)" (Deprotonation)
(H)
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Doping (Protonation)
>=N--
N=
