We have investigated a select group of amorphous aromatic polyimides to determine their potential suitability in fabricating thermally stable optical components, intended for use at high temperatures. Compared to current commercial polymers, these polyimides have much higher glass transition and decomposition temperatures, and also have much lower thermo-optic and thermal expansion coefficients. This combination of characteristics makes them potentially useful in a wide range of commercial and military applications. To better understand the optical properties of these polyimides, we have investigated correlations between several aspects of their chemical structures and their thermo-optical properties. Our study consisted of synthesizing variations of these polyimides, which incorporated targeted structural modifications, and then correlating these structures with trends observed in their optical properties. The modifications studied included the substitution of a variety of side groups that affect the low-frequency vibrational modes, the substitution of structural isomers with distinct symmetries, and the introduction of functional groups that alter the monomer-level anisotropy. Furthermore, we also investigated copolymerization in compatible pairs of monomers as a means of fine-tuning the thermo-optical properties.
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