High gas permeance in CO₂-selective thin film composite membranes from bis(phenyl)fluorene-containing blends with PIM-1

A novel approach to improve the initial performance as well as to prevent physical aging of superglassy high free volume polymer PIM-1 is reported. Bis(phenyl)fluorene-based polymer of intrinsic microporosity (Cardo-PIM-1) was used at different loadings to fabricate thin film composite (TFC) membranes and freestanding membranes. The gas performances of both TFCs and thick freestanding membranes exhibited similar trends; higher CO₂ permeance and higher CO₂/CH₄ selectivity at relatively low loadings (≤5 wt%). TFCs containing 5 wt % Cardo-PIM-1 achieved a CO₂ permeance of (12,600 ± 866 GPU), which corresponds to about a threefold increase as compared to the pristine TFC-PIM-1 membranes (2850 ± 254 GPU) and higher CO₂/CH₄ selectivity (14.57 ± 1.32) as compared to pure PIM-1 (10 ± 3). With regards to physical aging, PIM-1 TFC membranes experienced a 96 % reduction in CO₂ permeance after 1 year. However, for the TFCs containing 5 wt % cardo the reduction was considerably lower (59%) and all took place at an initial stage of up to 37 days, remaining at a good and stable CO₂ permeance of c.a. 5000 barrer for the remaining testing period of up to one year.