Influence of curing temperature on the optical properties of fluorinated polyimide thin films

The influence of curing temperature (CT) on the optical properties of 6FDA/ODA poly(amic acid)-polyimide (PAA-PI) films was characterized by measuring ATR-FT-IR spectra, refractive index (RI) and birefringence of the films. The results showed that the infrared absorption intensity of characteristic peaks (IAICP) corresponding to the imide ring and the RI of PAA-PI films reached their maxima when the films had been cured at 270 °C, while the magnitude of birefringence (|Δn|) of the films reached its minimum as CT rose up to 330 °C. However, the RI decreased as CT was between 270 °C and 330 °C. Both the RI and |Δn| of the film increased obviously when CT increased after 330 °C. We think this is due to the interchain crosslink reaction (ICCR) above 330 °C and can be an evident proof of ICCR. And the evidences supporting ICCR was also discussed via IR differential spectra.