(489b) Effects of Residual Solvent On Membrane Structure and Gas Permeation In a Polymer of Intrinsic Microporosity: Insight From Atomistic Simulation

Micro-structure and permeation in a polymer membrane are closely related to residual solvent during membrane fabrication. In this study, we conduct atomistic simulation to investigate the effects of residual solvent on free volume distribution and H₂ permeation in a polymer of intrinsic microporosity (PIM-1). The interaction energies of three solvents (CHCl₃, CH₃OH, and H₂O) with PIM-1 are predicted to be -16.3, -9.6 and -7.0 kcal/mol, respectively, in good agreement with available experimental data. On this basis, a structure-property relationship is proposed between interaction energy and the critical volume of solvent. The cyano and dioxane groups in PIM-1 interact preferentially with CH₃OH and H₂O; however, the carbon atoms interact more strongly with CHCl₃. The mobility of residual solvent is found to decrease in the order of H₂O > CH₃OH > CHCl₃. Upon comparison, the mobility of PIM-1 chains is small but facilitated by solvent due to the cooperative interaction between polymer and solvent. The fractional free volume and large voids in PIM-1/solvent membranes are observed to decrease as CH₃OH > CHCl₃ > H₂O, which is consistent with positron annihilation lifetime spectroscopy measurement. The solubility and diffusion coefficients of H₂ decrease in the same order, and the predicted and experimental coefficients are in fairly good agreement. This simulation study provides atomistic insight into the microscopic properties of residual solvent in a polymer membrane, and reveals that residual solvent play a crucial role in tailoring membrane structure and gas permeation.