THE IN-SITU SYNTHESIS OF PROTECTIVE COATINGS ON STEEL THROUGH A SURFACE SPONTANEOUS POLYMERIZATION PROCESS

This article reports a new method of forming protective coatings on me tal surfaces. The process is very simple and environmentally friendly. Polymerization occurs spontaneously on the metal surface after the im mersion of a cleaned metal substrate into a dominantly aqueous monomer solution. A layer of coating with uniform thickness is formed in situ . The coating thickness can be controlled from 1 to 50 mu m. This arti cle will describe the spontaneous polymerization process as it occurs specifically on steel and for a 4-carboxyphenyl maleimide-styrene mono mer system. The polymerization propagation mechanism is free radical, and alternating copolymers are always obtained in this system, even wi th significant changes in the monomer feed composition. This could be attributed to the formation of a charge transfer complex between the m onomer pair. The incorporation of the rigid imide ring into the copoly mer backbone significantly improves the coating's thermal properties, and styrene enhances the electrical properties. These properties are r elatively insensitive to the monomer feed composition, supporting the formation of alternating copolymer. The effects of several process var iables have been evaluated, including solution pH, monomer concentrati on, solution temperature, and monomer feed composition. The proposed i nitiation mechanism involves the direct electrochemical reduction of t he monomer by the steel surface to generate the initiating free radica ls. (C) 1997 John Wiley & Sons, Inc.