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

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