Synthesis of Surface-Metallized Polyimide Films via in Situ Reduction of (Perfluoroalkanoato)silver(I) Complexes in a Poly(amic acid) Precursor

Thermal curing of the silver(I)-containing poly(amic acid) formed from 3,3‘,4,4‘-benzophenone tetracarboxylic acid dianhydride (BTDA) and 4,4‘-oxydianiline (4,4‘-ODA) in dimethylacetamide leads both to polyimide films via cyclodehydration and to reduction of silver(I) giving a metallized surface. The resulting metallized composite films retain mechanical and thermal properties similar to those of the parent polyimide. Variation of the silver(I) additive and concentration and the thermal cure cycle allows the fabrication of silver layers which are both reflective and/or electrically conductive. Silver(I) trifluoroacetate and pentafluoropropanoate give excellent silvered films; however, higher perfluoroalkanoates such as silver(I) heptafluorobutanoate give films which are poorly surface metallized and extensively bubbled. X-ray diffraction shows crystalline face-centered cubic silver in the films after thermal curing. Microscopy data show that the surface particle sizes are in the range of ca. 100−500 nm. Significant silver remains in the bulk of the polyimide film with varying particle sizes generally less than ca. 15 nm. The interior of the metallized films is not electrically conducting. Films were characterized by X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy.