Opto-Thermal Characteristics of Amorphous Polyimides for Optical Applications
Journal Article - Open Access
NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States
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Polymeric components are desirable in optical and photonic applications because of their light weight. high impact resistance, andor ability to be formed into sophisticated shapes or gradient index GRIN optics. However, relatively large thermal effects in polymers can limit applications. We studied a selected series of amorphous polyimides in order to evaluate their potential application in components of optical devices. Several of these polyimides have thermo-optic coefficients dndT and volume coefficients of thermal expansion VCIh about 50 smaller than those of standard optical polymers, such as PMMA and polycarbonate. Surprisingly, these low dndT and VOTE values were found in amorphous polyimides which have sterically hindered, kinked linkages between phenyl rings. This suggests a different structural dependence than that found in previous studies, which showed that low thermal expansion in crystalline polyimides is correlated with a rigid linear backbone molecular structure. Thus, amorphous polyimides with favorable backbone structures represent a class of materials with improved thermo-optical stability for polymeric optical devices.