Palladium−Polyimide Nanocomposite Membranes:  Synthesis and Characterization of Reflective and Electrically Conductive Surface-Metallized Films

• Published in: Chemistry of materials 2005-04, Vol.17 (8), p.2091-2100
• Main Authors: French, B. L, Davis, Luke M, Munzinger, E. S, Slavin, J. W. J, Christy, P. C, Thompson, D. W, Southward, R. E
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm040378m

Palladium-surface-metallized polyimide films were prepared by an unusual macromolecular-matrix-mediated, single-stage synthetic protocol first reported by Taylor et al. (J. Am. Chem. Soc. 1980, 102, 876). Several Pd(II) complexes, [PdCl2(SMe2)2], [PdBr2(SMe2)2], and Pd(CF3COO)2, were dissolved in the poly(amic acid)s of 3,3‘,4,4‘-benzophenonetetracarboxylic acid dianhydride (BTDA)/4,4‘-oxydianiline (4,4‘-ODA) and 3,3‘-diaminobenzophenone (BPDA)/4,4‘-ODA in the solvent dimethylacetamide. Films cast onto glass plates from these Pd(II)-doped resins were thermally cured to 300 °C in air, which resulted in air-side surface-metallized membranes. The films were characterized by both specular and diffuse reflectivity and by conductivity measurements as a function of the cure time and temperature. Maximum specular reflectivities of ca. 50% were observed at 530 nm. After maximum specular reflectivities were achieved in the thermal cure cycle at 300 °C from 0.5 to 2 h, the film surface quickly degraded upon further curing. The surface sheet resistivities were in the range of ca. 1−75 Ω/square. Initial Pd metal particles formed in the film were in the 3−10 nm range. The optical data coupled SEM micrographs, elemental analytical results, and X-ray diffraction observations were interpreted to support a mechanism for the formation of a reflective and conductive metallized surface which involves selective air-side surface oxidative degradation of the polyimide matrix to volatile products, which then concentrates the metal nanoparticles at the surface and increases the particle size via sintering. The mechanical properties of the metallized films are compromised with respect to the parent polyimide although the composite membranes are still useful for a range of applications. The tensile strength is reduced; the percent elongation and the tensile modulus are increased. Both BTDA/ODA and BPDA/ODA gave very similar results with the Pd(II) additives. Many Pd(II) compounds, e.g., PdBr2, were not useful in generating a metallized surface, which suggests that the pathway to a metallized surface is extremely sensitive to the experimental conditions.