Free volume and gas transport properties of hydrolyzed polymer of intrinsic microporosity (PIM-1) membrane studied by positron annihilation spectroscopy.

In this work, a series of hydrolyzed polymers of intrinsic microporosity (PIMs) membranes were successfully synthesized under alkaline conditions. Positron annihilation lifetime measurement is employed to analyze the pore structure of the hydrolyzed PIMs. In the original PIM-1, there are two kinds of pores, i.e. micropores with radius of 4.32 Å and ultramicropores with radius of 2.58 Å. The size of all the pores shows a continuous decrease with increasing hydrolysis time, which is confirmed by the reduced chain-to-chain spacing in the hydrolyzed PIMs measured by X-ray diffraction. Meanwhile, the fractional free volume also shows decrease after the hydrolysis process, while the relative number of ultramicropores increases. Benefiting from the smaller pore size in the hydrolyzed PIMs membrane, the gas molecules with smaller size (such as CO 2) can be separated more efficiently. The selectivity of CO 2 /CH 4 of hydrolyzed PIMs reaches up to 30.05 with a relatively high CO 2 permeability of 140.58 Barrer, which exceeds the Robeson's 1991 upper bound. Our results indicate that the hydrolyzed polymers of intrinsic microporosity membranes are promising candidates for gas separation membrane in the future. [Display omitted] • A series of hydrolyzed PIMs membranes were synthesized under alkaline conditions. • The process shortens the reaction time and improves the gas separation performance. • The logarithm of P shows a linear relationship with 1/FFV. • Positron lifetime measurements indicate the free volume adjusts the selectivity. [ABSTRACT FROM AUTHOR]