Polyimide/metal composite films via in situ decomposition of inorganic additives: Soluble polyimide versus polyimide pre
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. INTRODUCTION Polymer-metal composites in which submicron metal or metal oxide domains have been incorporated in a polymer matrix by the in situ thermal or electromagnetic radiation promoted decomposition of metal-containing additives may yield superior, more uniform materials than conventional heterogeneous composite formation techniques. In addition, the decomposition and phase separation of the additive could result in structurally interesting polymer-metal composites. Furthermore, molecular composites that possess unusual spectroscopic, electrical, magnetic, mechanical, and catalytic properties may be feasible. This approach to the preparation of polymer-metal composites may also afford unique opportunities for investigating fundamental aspects of nucleation and growth of metal and metal oxide clusters in the solid state. In situ decomposition of inorganic additives to produce metal or metal oxide in a polymer matrix is a relatively new synthetic approach. Most investigations in this regard have concentrated on polyimides and moderately reactive inorganic additives (e.g., simple salts and complexes). This work had its beginnings approximately 30 years ago when Angelo1 briefly reported in a patent the addition of metal ions to several types of polyimides. The object of the invention was a process for forming particle-containing ( < 1 /j,) transparent polyimide structures. More recently a wide variety of additives representing numerous elements have been employed to successfully modify polyimide properties.2 For example, the incorporation of a palladium complex into a polyimide produced a film with a reflective metal surface and increased the surface conductivity by over ten orders of magnitude3 compared with the nondoped control. Highly reflective films were also produced 996
J. Mater. Res. 3 (5), Sep/Oct 1988
http://journals.cambridge.org
when certain copper compounds were used as dopants, although increased conductivity was not observed.4 Metal incorporation was also used to enhance the mechanical5 and adhesive6 properties of polyimides. The general scheme used to produce these modified polymers involved the initial reaction of a diamine with a dianhydride in an appropriate solvent. The resulting polyamide acid was then mixed with a soluble metal species. A thin film of the homogeneous solution was cast and then heated to effect imidization and produce the metal-containing polyimide film. Most of the doped polyimide films exhibit a unique feature in that one side contains a tightly adhering, readily observable deposit that originates during the thermal imidization process. In each case the resulting surface deposit is derived from the chemical dopant. Two patterns of reactivity have generally been observed: conversion of the additive to the metallic state (Pd, Pt, Ag, Au) or conversion to a metal oxide (Li 2 O, CuO, SnO 2 , Co 3 O 4 ). For standard doping levels (1:4 mole ratio, dopant to monomer) the metal or metal oxide prefers solely the air side of the film, except for certain gold-containing polyimides
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