Treatment of conversion-coated metal substrates with preformed reaction products of catechol compounds and functionalized co-reactant compounds

A method, comprising contacting a surface of a metal substrate having a conversion coating layer thereon with an aqueous mixture comprised of at least one preformed reaction product of at least one catechol compound and at least one co-reactant compound comprised of one or more functional groups reactive with the at least one catechol compound to thereby deposit a seal layer comprising the at least one preformed reaction product on the conversion coating layer;

• wherein the at least one co-reactant compound comprises at least one linear or branched, oligomeric or polymeric polyethyleneimine having a number average molecular weight of 500 up to 2,000,000, wherein the at least one catechol compound includes at least one amino-functionalized catechol compound or salt thereof, and wherein the pre-formed reaction product comprises 5 to 25% by weight of the at least one catechol compound, based on total weight of the at least one catechol compound and the at least one co-reactant compound.