Colorless and Transparent Copolyimide Nanocomposites

Abstract

Copolyimides (Co-PIs) were synthesized from 2,2'-bis(trifluoromethyl) benzidine (TFB) and different ratios of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and pyromellitic dianhydride (PMDA). The Co-PI films were obtained from poly(amic acid) (PAA) by solution-casting through typical chemical and thermal imidizations. The thermal properties and optical transparency of the Co-PI films with various PMDA monomer contents were investigated. It was found that with increasing PMDA content, the thermal transition temperatures of the Co-PI films increased. Co-PI nanocomposites were prepared with various amounts of organically modified hectorite (STN) on a TFB:6FDA:PMDA = 1.0:0.9:0.1 mole ratio Co-PI hybrid film to examine the thermal properties, morphology, and optical transparency. The thermo-optical properties of the Co-PI hybrid films deteriorated with increasing clay content. However, the coefficient of thermal expansion (CTE) and oxygen barrier properties of the PI hybrid films improved with increasing clay content.