Effect of Nonsolvent Treatments on the Microstructure of PIM-1

The combination of appreciable swelling at unit activity sorption, weak polymer–penetrant interactions, and high vapor pressure allows methanol to be effective at restoring free volume to glassy polymers compared to similar organics. Polymers of intrinsic microporosity (PIMs) are often soaked in methanol and then dried before permeation and sorption analysis to improve reproducibility and eliminate processing history. Here, surface area, pore volume, thermogravimetric analysis, sorption, and diffusion data are used to demonstrate the effectiveness of methanol treatments at removing nonsolvent-induced changes to PIM-1, specifically using dimethylformamide (DMF) as a candidate conditioning molecule. DMF clearly plasticizes PIM-1 while methanol does not. In addition, diethyl ether-conditioned PIM-1 showed marked increases in surface area and free volume—higher than that found from methanol conditioning. Strongly plasticizing nonsolvents with low vapor pressures can be used as conditioning agents that promote polymer relaxations, accelerate chain packing, and remove additional nonequilibrium free volume.