Thermostable birefringent copolyimide films based on azobenzene-containing pyrimidine diamines

Abstract

Azobenzene (azo)-containing polymers have attracted continuous attention due to their excellent photosensitivity. However, practical applications of their photo-induced birefringence have been hampered by low thermal stability. In this work, we report a series of polyimides synthesized by a low-temperature co-polycondensation of azo-containing pyrimidyl diamine, 4,4′-diaminodiphenyl ether, and 4,4′-oxydiphthalic anhydride. The obtained co-polyimides (co-PIs) show good thermal stability, with high glass transition temperatures (T_g) of more than 200 °C and 5% weight loss temperatures (T_5%) as high as about 400 °C in nitrogen. Their photo-induced birefringence (Δn) has been determined as 0.013 at room temperature and up to 0.017 at 100 °C. The photo-induced reorientation property of the as-prepared highly thermostable azo-PIs is expected to have wide applications in image recording and electro-optical devices.