UV‐Rearranged PIM‐1 Polymeric Membranes for Advanced Hydrogen Purification and Production

Abstract

Abstract Polymers of intrinsic microporosity (PIM‐1) have been known for their super high permeability but average selectivity for medium‐size gas pairs. They have unimpressive selectivity for H 2 and CO 2 separation (i.e., α (H 2 /CO 2 ) = 0.6). For the first time, we have discovered that ultraviolet (UV)‐rearranged polymers of PIM‐1 membranes can be used for H 2 /CO 2 separation with far superior separation performance to others in literatures. The PIM‐1 membrane after UV radiation for 4 hours shows H 2 permeability of 452 barrer with H 2 /CO 2 selectivity of 7.3. Experimental data and molecular simulation reveal that the polymer chains of PIM‐1 undergo 1,2‐migration reaction and transform to close‐to‐planar like rearranged structure after UV radiation. As a result, the UV‐irradiated PIM‐1 membrane shows considerable drops in both fractional free volume (FFV) and size of micro‐pores. Positron annihilation lifetime (PAL) results have confirmed the chemical and structural changes, suggesting the FFV and pore size drops are mainly ascribed to the destructed spiro‐carbon centre during UV radiation. Sorption and x‐ray diffractor (XRD) analyses indicate that the impressive H 2 /CO 2 selectivity arises from the significantly enhanced diffusivity selectivity induced by UV radiation, followed by molecular rearrangement, conformation change and chain packing.