A novel process to form protective polymer coatings on aluminum using spontaneous polymerization is described. When an aluminum sample is immersed in a partly aqueous monomer solution, polymerization proceeds rapidly on the metal surface, without the addition of initiator, at room temperature. The polymer coatings studied here were formed using styrene (St), N‐phenyl maleimide (NPMI), 2‐methacryloyloxy acetoacetate (MEA), and bis‐maleimide (BMI), monomers, from solutions of different compositions. A possible mechanism for spontaneous initiation and propagation is proposed. The effects of process variables such as polymerization time, monomer concentration, and monomer ratios in feed on the coating thickness and properties are presented. The glass transition temperatures, adhesion strength to aluminum, thermal stability and corrosion resistance of these coatings are reported. The coatings obtained are up to 50 μm thick and conform to the shape of the substrate. They have excellent thermal stability, low dielectric constant, and show very good resistance to corrosion under the ASTM B‐117 accelerated salt fog test. Other monomers and metals may also be used.

Spontaneous polymerization to give conformal, uniform coatings on metals has been expanded to a series of different monomers. The monomer 4-fluoro maleimide, when copolymerized with styrene, a coupling agent, and a bis-maleimide crosslinker, imparts very low dielectric constant (2.4) to the coating while retaining high temperature resistance. Diethyl fumarate, with the same comonomers, enhances ductility and provides an adjustable glass transition temperature. Addition of glycidyl acrylate to the monomer system provides reactivity of the coating to epoxy resins. Kinetic studies using these monomers were consistent with the free radical polymerization mechanism. The rate of reaction seemed limited by the diffusion of species to the reaction site. Extent of incorporation of the new monomers into the chain backbone was verified, and adhesion and corrosion resistance properties examined. The data illustrate the versatility of the conformal, chrome free spontaneous polymerization process.

No abstract

Electropolymerization has been used as a method to form polymers on graphite fibers and metals. Most of the previous studies have involved either the use of sulfuric acid as an initiator or direct reduction or oxidation of monomers to form the polymers. In this article, ␣-bromoisobutyronitrile (BrIBN) was used as a new electrochemical initiator to form polymer coatings on an aluminum cathode. The reduction of BrIBN on a glassy carbon electrode was examined using cyclic voltammetery. It was found that BrIBN could be reduced to isobutyronitrile radicals at potentials below the reduction potential of water. The reduction behavior of BrIBN was found to be similar in aqueous, semiaqueous, and nonaqueous solutions. 2-Methacryloyloxy(ethyl) acetoacetate was then electropolymerized on aluminum using the BrIBN as the initiator and lithium perchlorate as a supporting electrolyte. Defect-free coatings were formed at half-cell potentials of less than Ϫ1.20 V. The effect of various process variables on the polymerization kinetics under potentiostatic conditions is reported. The coating thickness increased with polymerization time, monomer concentration, and initiator concentration. A strong dependence of thickness on monomer concentration was observed. As expected, there was weak dependence on the initiator concentration.

No abstract