Simple and easy recycling of poly(amic acid) gels through microwave irradiation

Poly(amic acid)s (PAAs), which are precursors of polyimides, often undergo gel formation during their synthesis or storage, and these insoluble gels have been discarded. In this work, we discovered that the gels could be converted to homogeneous PAA solutions by fast and simple microwave (MW) irradiation. The PAA gels were placed inside a domestic MW oven, and MW irradiation was carried out with 240 W for 2 min. The recycled PAA solutions afforded polyimide films, coatings, and powders. The polyimides prepared from the recycled PAA solutions exhibited higher glass transition temperatures (T_gs), decomposition temperatures, and char yields than comparison polyimides obtained from ordinary PAA solutions. Flexible free‐standing polyimide films were obtained by drop‐casting of the MW‐treated solutions and subsequent thermal imidization. Mechanical properties and dielectric constants were measured for the polyimide films and coatings, respectively. This new method has significant advantages for the environment, economy, and industry. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 981–987