Adamantane-grafted polymer of intrinsic microporosity with finely tuned interchain spacing for improved CO2 separation performance

Polymers of Intrinsic Microporosity (PIMs) based gas separation membranes usually possess high CO2 permeability but suffer from relatively low selectivity. Post modification by polar groups could increase selectivity but often loss of permeability. In this work, adamantane is grafted onto amidoxime-functionalized PIM-1 (AOPIM-1) mainchain through a simple acyl chloride-substitution reaction. As a side group, adamantane is used to adjust the chain packing of AOPIM-1 and thus affect the permeability of gases, especially CO2 permeability. Our results show that the d-spacing of adamantane-grafted AOPIM-1 membranes could be finely tuned by adjusting the mole ratio of grafted adamantane moiety on the polymer. The obtained membrane exhibits significantly enhanced CO2 permeability from 980.7 barrer in the case of AOPIM-1 membranes to 2483.6 barrer in the case of adamantane-grafted AOPIM-1 membranes, while the selectivity of CO2/N-2 and CO2/CH4 gas pairs are 31.2 and 30.1, correspondingly. The comprehensive separation performance of adamantane-grafted AOPIM-1 membrane for CO2/N-2 and CO2/CH4 largely surpasses the Robeson upper bound.