Electroless metallization of organic polymers using the polymer as a redox reagent: Reaction of polyimide with zintl anions

A facile general scheme for the metallization of polyimides (PIm) and certain other organic polymers is presented. The driving force for the metallization is the extremely strong reducing power of the polyatomic main group anions, the so-called Zintl anions.The polymide can be metallized with many main group elements (e.g. germanium, tin, lead, arsenic, antimony), by simply treating the PIm with solutions obtained from the extraction of potassium-main group alloys. The metal films are formed by the topochemical oxidation of the anionic clusters by the polyimide. The reaction proceeds by a reduction-intercalation-deposition mechanism where the PIm is reduced to monoanions and dianions, the Zintl anion's alkali metal counteraction intercalates the polymer to balance the charge from the reduction and the clusters are oxidized to the metallic state on the polymer surface.The polyimide metallization has been extended to certain transition metals by employing a method that is conceptually the reverse of main group metallizations discussed above (i.e. using the PIm as a reducing agent toward an oxidized metal species in solution). Specifically, the treatment of PIm with methanol solutions of K₄SnTe₄ gives intercalated material, K_x·PIm, with no surface metallization. The reaction of K_x·PIm with solutions of transition metal cations with reduction potentials more positive than that of K_x·PIm results in metal deposition.The preparation of surfaces containing two metals, by a combination of the two above methods, will be discussed.