Effect of charge transfer and chain stacking on the optical and thermal properties of polyimides derived from sulfone and amide-containing dianhydride

To study the effect of charge transfer and chain stacking on the optical and thermal properties, a group of polyimides (PIs) were prepared from various diamines and dianhydrides containing sulfone, amide, and/or trifluoromethyl groups. Ultraviolet–visible spectroscopy, thermomechanical analysis, and thermogravimetric analysis were employed to study the properties of PIs. PIs containing sulfone and amide groups exhibited transmittance varying from 2.9% to 44.9% at 400 nm with good thermal stabilities of 5% weight loss in nitrogen at 455–466°C. The coefficient of thermal expansion values were 37.7–49.8 ppm/°C and glass transition temperatures were 261–299°C. The improved optical properties are owing to incorporation of amide group that decreases the electron-acceptability and sulfone group that distorts the chains, inhibiting the dense chain stacking. There is a trade-off relationship between the optical property and thermal property.