Highly permeable and aging resistant 3D architecture from polymers of intrinsic microporosity incorporated with beta-cyclodextrin

Abstract

The polymers of intrinsic microporosity (PIM) incorporated with beta-cyclodextrin (β-CD) (referred to as PIM-CD) are prepared to investigate the effects of unique 3-dimensional (3D) hollow bowl structure of β-CD on gas separation performance and physical aging behavior. Compared with the pristine PIM membrane, the permeability of PIM-CD membranes increases with an increase in β-CD loading. Pure gas permeation tests reveal that the incorporation of a very small amount of β-CD into the PIM matrix can significantly enhance the CO2 permeability from 3368 to 8812 barrer, an increase of 162%, without too much sacrifice of gas selectivity. The gas separation performance of PIM-CD membranes can surpass the Robeson upper bound lines for almost all of the gases. Analyses from positron annihilation lifetime spectroscopy and wide angles x-ray diffraction confirm that the β-CD incorporation brings PIM-CD membranes with bigger micro-pores and higher fractional free volume, resulting in a higher gas permeability. In addition, the interactions between β-CD and PIM can restrict chain movement and make ultra-fine micro-pores difficult to collapse. Thus the PIM-CD membranes exhibit much greater resistance to physical aging than PIM membrane. These results may open up new avenues for molecular design of 3D architecture CD-based membranes for gas separation.