Polyimide blend metal–organic framework‐based mixed matrix membrane for gas separation: A review

Abstract Polyimide (PI), a glassy polymer, suffers from permeability–selectivity trade‐off and plasticization, which restrict its gas separation performance. Instead of exploring new materials, polymer blend and mixed matrix membrane (MMM) emerge as promising approaches in improving membrane gas separation efficiency attributed to their simplicity and cost efficiency. However, polymer immiscibility and polymer‐filler incompatibility are the main challenges encountered in these two approaches, respectively. Thus far, only limited reviews target the comparison between PI/glassy and PI/rubbery polymer blends. Besides, the review on improving the compatibility between polymer and filler in PI‐metal–organic framework (MOF) MMM is also lacking. Hence, this review aims to assess the gas separation characteristics of PI blended with glassy and rubbery polymers, focusing on the blend miscibility. It was discovered that the casting solvent's solubility parameter and solvent volatility play a part in governing the blend miscibility. Meanwhile, the efficiency of surface functionalization and ionic liquid addition in improving the polymer–filler compatibility in MMM is also reviewed. The wet method for filler incorporation demonstrates a more homogeneous filler dispersion within the membrane. Hence, its employment in MOF‐based MMM fabrication can be explored further.