Forming protective coatings on aluminum using spontaneous and electro polymerization

Date of Completion

January 1997


Chemistry, Polymer




Two novel methods of polymerizing conformal protective coatings onto aluminum have been developed, and are described. A novel process to form protective polymer coatings on aluminum using spontaneous polymerization was developed. When an aluminum sample is immersed in a partly aqueous monomer solution, spontaneous initiation and polymerization occurs 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 reported. The glass transition temperatures, adhesion strength to aluminum, thermal stability and corrosion resistance of these coatings were measured. The coatings obtained are up to 50 $\mu$m thick and conform to the shape of the substrate. Other monomers were also incorporated into the polymer, to modify the properties of the coating.^ Electropolymerization has been used as a method to form polymers on graphite fibers and metals. In this work a novel initiation scheme was developed, using $\alpha$-bromoisobutyronitrile (BrIBN) as an electrochemical initiator to form polymer coatings on aluminum cathode. The reduction behavior of BrIBN on glassy carbon electrode was studied using cyclic voltammetery. It was found that BrIBN could be reduced to isobutyronitrile radicals, which initiated polymerization on the aluminum surface, at potentials below the reduction potential of water. 2-methacryloyloxy(ethyl) acetoacetate (MEA) was electropolymerized on aluminum using the BrIBN initiator. The coating thickness increased with polymerization time, monomer concentration and initiator concentration. While a strong dependence of thickness with monomer concentration was seen, a weak dependence was seen on the initiator concentration. Copolymers of Acrylonitrile (AN) and Methyl Acrylate were also formed, and the resulting polymer-metal interface was characterized. ^