Synthesis, characterization, and electropolymerization of mannich bases: Influence of substituents on protective ability of organic coatings

Aminoalkyl phenol derivatives were prepared and tested for electrooxidation in alkaline hydroalcoholic electrolytes. We estimated the relative insulat ing character of thin (<0.3 mu m) organic coatings on several metal electro des (Fe, Cu, and Ni), through both voltammetric and potentiostatic runs. Un saturated allyl and but-3-enyl groups confer the mast effective passivation phenomenon, while N-methyl-substituted Mannich bases do not provide the go od protective properties expected. This result was explained through the re lative easiness of the nitrogen oxidation of these monomers, leading to par asite reactions (methoxylation of the growing polymer chains) and additiona l termination reactions, thereby limiting the molecular weight of the polym er. FTIRAS results showed that products of the anodic oxidative coupling pr ocess consist (especially for the nature of monomer) of a poly(oxy-1,4-phen ylene)-type structure. Amino and unsaturated substituted groups remain unch anged during electropolymerization, making the resulting coatings attractiv e to use as reactive primer layers. The thickness of the coatings was found to reach 2-5 mu m in free-water solutions. This behavior, particular to Ma nnich bases, was explained by the hydrophilic character of the growing poly mer chains due to the presence of amino groups. (C) 2000 John Wiley & Sons, Inc.