Synthesis, properties, and molecular simulations of high‐barrier polyimide containing carbazole moiety and amide group in the main chain

Abstract

AbstractAn intrinsic high‐barrier polyimide (2,7‐CPAPPI) containing rigid planar carbazole moiety and amide group in main chain was prepared. The 2,7‐CPAPPI shows very attractive barrier performances, possessing water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) low to 0.04 g m−2 day−1 and 0.11 cm3 m−2 day−1, respectively. Meanwhile, 2,7‐CPAPPI also displays exceptional thermal stability with a glass transition temperature (Tg) of 552°C and coefficient of thermal expansion (CTE) of 15.48 ppm/K. The barrier performances of 2,7‐CPAPPI are compared with those of a structural analog (2,7‐CPPI, containing only carbazole moiety in the main chain) and a typical polyimide (Kapton). The structure–barrier performances relationship was investigated by molecular simulations, wide angle X‐ray diffraction (WAXD), and positron annihilation lifetime spectroscopy (PALS). The results show that 2,7‐CPAPPI has more number of intermolecular hydrogen bonds among the three PIs, which leads to close chain packing and thereby high crystallinity, low free volume, and poor chains mobility. That is, the high crystallinity and low free volume of 2,7‐CPAPPI decrease the diffusion and solubility of gases. Meanwhile, the poor chains mobility further reduces the gases diffusion. The decreased diffusion and solubility of gases consequently promote the improvement of barrier properties for 2,7‐CPAPPI.