Enhancement of Dimensional Stability in Soluble Polyimides via Lanthanide (III) Additives

Abstract

A need exists for optically clear thin films which can endure for long periods in a space environment for applications on large-area solar collectors, inflatable antennas, solar arrays, and various space optics. Fluorine-containing polyimides such as those derived from 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 6FDA, are excellent candidates for use in space due to their high optical transparency at the solar maximum wavelength of 500 nm, their outstanding resistance to radiation, and many other properties.^1-8 These polymers, however, generally display coefficients of thermal expansion (CTE) between 40 and 50 ppm. Because dimensional stability of large space structures is critical to performance and efficiency, it is desirable to lower the CTE of these polymers. The control of CTE and the ability to match the CTE of polyimides to those of inorganic materials in composite devices is of considerable challenge and interest.⁹ Preliminary studies have shown that the CTE of fluorine-containing polyimides can be lowered by as much as 30 percent by the addition of modest quantities of lanthanide (III) compounds.^{10, 11, 12}