Continuous microflow synthesis of dimethyl-substituted cyclobutanetetracarboxylic dianhydrides and its application on polyimide films

The combination of continuous-flow microreactors and photoreaction is one of the important researches in flow chemistry. Dimethyl-substituted cyclobutanetetracarboxylic dianhydride (DM-CBDA) was prepared through photodimerization in photomicroreactors and applied in the preparation of polyimide films. It was found that ethyl acetate as the solvent and an appropriate concentration of substrate could benefit this photodimerization process in the capillary photomicroreactor. Higher photonic efficiency and higher DM-CBDA yield were obtained in the photomicroreactor as compared to batch photoreactors. DM-CBDA was applied to prepare the colorless transparent polyimide films, which showed a high polymerization activity for the preparation of poly(amic acid) with high molecular weight. A PI film of DM-CBDA/ODA with the UV cutoff wavelength of 295 nm, the glass transition temperature of 376 °C, and the elongation at break of 11.3% was prepared. This work broadens the application of photomicroreactors for the preparation of polyimide monomers in flow chemistry and its films with good transparent, thermal and mechanical properties.