Abstract

High-performance polymers for membrane gas separation require the careful design of the structure-porous relationship. In this work, five phthalimide-based polymers of intrinsic microporosity (PIMs) were obtained via the double nucleophilic aromatic substitution with the commercially available 5,5?,6,6?-tetrahydroxy-3,3,3?,3?-tetramethylspirobisindane (TTSBI) monomer. The phthalimide monomers were synthesized considering different sizes and positions of the alkyl-substituents to evaluate their influence on the physical properties of the polymers and their potential use as gas separation membranes. Four polymers were soluble in the low-boiling solvents chloroform and tetrahydrofuran, facilitating the casting of self-standing films to evaluate their gas separation properties. The thermally stable membranes showed 5% weight lost between 537 °C and 549 °C. As powders, these four polymers showed apparent BET surface areas ranging from 434 to 661 m2 g?1. The experimental BET surface areas correlated with those obtained by molecular simulation models of the synthesized polymers. A linear function is proposed as a tool to predict, with a known uncertainty, the surface area values of this type of polymer from the corresponding computational models. As a trend, increasing the volume of the ortho-substituent in the aryl-phthalimide group increases the permeability of the membranes, reaching generally better performances than Matrimid® and close to those of PIM-1, considering their place on the Robeson diagrams of the O2/N2, CO2/CH4 and CO2/N2 gas pairs. Aging studies between 63 and 122 days showed a decrease in permeability, accompanied by the typical increase in selectivity that tends to move the data parallel to the upper Robeson limits. © 2023 The Royal Society of Chemistry.