Synthesis, gas barrier and molecular simulation of intrinsic high-barrier polyimide bearing carbazole and amide

Abstract

A novel diamine (3,6-CAPDA) bearing carbazole and amide group was prepared. On the basis of 3,6-CAPDA and pyromellitic dianhydride (PMDA), a high-barrier polyimide (3,6-CAPPI) was obtained through a two-step polymerization method. The 3,6-CAPPI displays excellent barrier performances and thermal stability. Its oxygen permeability (OP) and water vapor permeability (WVP) are low to 2.63 cm3·mil·m−2·day−1 and 3.22 g·mil·m−2·day−1, respectively. The 5% weight-loss temperature (Td5%) and glass transition temperature (Tg) are up to 526 °C and 431 °C, respectively. Through a combination of molecular simulation, X-ray diffraction and positron annihilation test, the effet of polymer structure on the barrier properties are fully explored. The results demonstrate that the introduction of carbazole and amide groups not only improves the chain order and rigidity, but also enhances the interchain force of polyimide, which thereby bring about enhancement of crystallinity and decreases of free volume and chain movement of 3,6-CAPPI. These factors lower the gas diffusivity and solubility in polymer matrix. Simultaneous decreases of gas diffusivity and solubility give rise to the notable enhancement of gas barrier for 3,6-CAPPI.