Title

Synthesis of protective coatings on steel by electro and surface spontaneous polymerization

Date of Completion

January 1997

Keywords

Chemistry, Polymer|Engineering, Materials Science

Degree

Ph.D.

Abstract

This work involves the development of two novel coating techniques for forming protective coatings on steel in-situ. The Surface Spontaneous Polymerization process (S-Poly) was discovered and developed in this laboratory. Polymerization occurs spontaneously on steel after immersion into a monomer solution, forming a layer of uniform and conformal coating, with thickness ranging from 1-50 microns. The proposed initiation mechanism involves the electrochemical reduction of the monomer by the substrate to generate the propagating free radicals. Aluminum, copper and several other easily oxidizable metals may also be used. Copolymerization of various monomers is possible to yield coatings with desired properties. Propagation can occur through both a charge transfer complex and free monomers. Several process variables have been identified and their effects on process kinetics and polymer molecular weight evaluated. These variables include reaction time, monomer concentration, solution temperature, solution pH, and monomer feed composition. A monomer system of phenyl maleimides/styrene/bismaleimide/(methacryloyloxy)ethyl acetoacetate has been developed. The coatings obtained have excellent thermal and dielectric properties, and good adhesion to steel. Corrosion resistance of a 4-carboxyphenyl maleimide (4CMI) coating, as measured by ASTM B-117, is excellent after 700 hours of salt spray test.^ The electropolymerization of 4CMI/styrene system has been successfully used to give temperature resistant, conformal insulating coatings on steel. N-methy-2-pyrrolidone was selected as the solvent for 4CMI to replace the toxic N,N-dimethylacetamide previously used. A polymerization cell with controlled flow was constructed to minimize the concentration gradient buildup in the solution, of interest for both electropolymerization and S-Poly.^ A series of arenediazonium salts were studied as possible electrochemical initiators, all of which have a reduction potential lower than that of water. Under typical reaction conditions the reduction efficiency of 4-methoxybenzenediazonium tetrafluoroborate (MBDT) is estimated to be 20.7%, using UVNIS. The electrocopolymerization of methyl acrylate and acrylonitrile on steel was successfully initiated using MBDT to afford smooth and uniform coatings. Both cyclovoltammetry and RAIRS results suggest that a strong interaction exists between the substrate and the initiator, which should lead to very good coating adhesion to the substrate. ^