Sorption and Diffusion of Organic Vapors into PIM-1 and the Effects of Methanol Conditioning

Polymers of intrinsic microporosity (PIMs) are of great interest for fluid separation membranes due to their high permeability and moderate selectivity. To improve reproducibility, high free volume polymers such as PIMs are often soaked in methanol and subsequently dried before permeation and sorption analysis. This methanol preconditioning step is believed to remove residual solvent trapped within the microstructure of the polymer as well as erase the past thermal processing history. However, few studies have carefully investigated this process. Sorption data is analyzed to determine the diffusion coefficients of DMF and methanol in neat PIM-1 as a function of volume fraction. Repeated sorption isotherms of organics without methanol treatment show evidence of membrane conditioning and reduced solvent uptake over time. This work examines the efficacy of methanol treatments to remove high boiling solvents such as DMF from PIM-1. Surface area, pore volume, and thermogravimetric analysis are used to quantify the effectiveness of the methanol treatment at erasing the processing history of the polymer.