Matrimid Membranes from Solutions in Thymol-Based Solid Solvents

Polyimides are valued for their high thermal and chemical stability, making them an important membrane material for gas separation. Among them, Matrimid 5218 is particularly permeable to hydrogen over other gases. Membrane fabrication is primarily a solution process that utilizes large volumes of solvents, raising significant environmental and health concerns. Developing sustainable alternatives without compromising performance is a major challenge. Here, we introduce a bioinspired hydrogen-bonding strategy to dissolve Matrimid 5218 using natural solvents. We demonstrate that thymol and its mixtures with menthol and vanillyl alcohol form directional hydrogen bonds with the polymer’s carbonyl group, disrupting interchain interactions and enhancing solubility. The role of these green solvents, analogous to that of eutectic mixtures, was elucidated by thermal, rheological, and advanced spectroscopic techniques. Detailed 1D and 2D NMR analysis revealed how hydrogen-bonding interactions weakened polymer–polymer associations during dissolution, enabling the preparation of integral porous asymmetric membranes with a thin and highly selective separation layer. The resulting membranes achieve a gas separation performance comparable to those prepared with conventional toxic solvents. This work successfully demonstrates natural solid solvents for the fabrication of polyimide membranes for hydrogen separation and other applications.