HIGH-TEMPERATURE AROMATIC POLYIMIDE FIRM DISPLAYING NONLINEAR-OPTICAL2ND-HARMONIC GENERATION BASED ON THE APPROACH OF THE POLED GUEST-HOSTSYSTEM

A segmented rigid-rod polyimide has been synthesized from 2,2'-bis(3,4 -dicarboxyphenyl)hexafluoropane dianhydride (6FDA) and 2,2'-trifluorom ethyl-4,4'-diaminobiphenyl (PFMB) in m-cresol at elevated temperature in a one-step polymerization. This aromatic polyimide (6FDA-PFME) is s oluble in a variety of organic solvents. 6FDA-PFMB has a glass-transit ion temperature (T-g) of 344 degrees C and a high optical transmission above 375 nm. The refractive indices along the in-plane and the out-o f-plane directions are different and show a negative birefringence. Bo th of the refractive indices decrease with increasing wavelength. When the non-linear optical guest molecule, 2-(p-nitrophenyl)-4,5-bis(p-hy droxyphenyl) oxazole (TNON) is doped into the 6FDA-PFMB matrix, phase separation does not occur below a 25% w/w concentration of TNON. The T -g of the guest-host system decreases with increasing TNON concentrati on. After corona poling, second-harmonic generation is retained up to 300 h at 80 degrees C. Even after the film is annealed at 200 degrees C for 0.5 h, a measurable fraction of the second-harmonic non-linearit y is retained.