Synthesis of hexafluoroisopropylidene-containing polyimide-silver nanocomposite films evolving specularly reflective metal surfaces

Abstract

Highly reflective surface-metallized flexible polyimide films have been prepared by the incorporation of the soluble silver ion complex (1,1,1-trifluoroacetylacetonato)silver(I) into dimethylacetamide solutions of the poly(amic acid) prepared from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (4-BDAF). Thermal curing to 300 °C of solution cast silver(I)poly(amic acid) films leads to cycloimidization of the amic acid with concomitant silver(I) reduction and formation of a reflective surface-silvered film from 6–13% weight percent silver. The reflective surfaces evolve only when the cure temperature reaches 300 °C. After achieving a maximum value the reflectivity abruptly drops with further heating at 300 °C and the polyimide suffers oxidation degradation. The metallized films are thermally stable and maintain mechanical properties similar to those of the parent polyimide. TEM reveals that the interior of the composite films have ca. 5–20 nanometer-sized silver particles. SEM shows surface silver particles from ca. 50–1000 nm whose size varies with cure time at 300 °C. Neither the bulk nor the surface of the films is electrically conductive. There is strong interfacial adhesion of metal to polyimide.