Polymers of Intrinisic Porosity with Bulky Side Groups on the Spirobisindane Moieties for Gas Separation

The polymer of intrinsic microporosity (PIM-1) for gas separation has attracted wide attention because of its high gas permeabilities and modest selectivities. In recent years, with the aim of further improving the gas separation performance, physical aging resistance, and plasticization resistance, abundant efforts have been made to functionalize PIM-1, either by modifying the nitriles or the hydrogens of the benzene ring in spirobisindane moieties. In this paper, the hydrogens of the benzene ring in spirobisindane moieties of PIM-1 were replaced with two bulky groups, pyrrolidinated methyl and 4-methylpiperidinated methyl, by the classical Mannich reaction and two PIM-based polymers, PIM-Py and PIM-MePi, were obtained. It is found that the bulky side groups in PIM-Py and PIM-MePi mainly fill the larger microporous region, while the ultramicroporous side groups had little changes. Therefore, the gas permeabilities of PIM-Py and PIM-MePi were lower than PIM-1, and the selectivities have slight increases (CO2/CH4 and CO2/N2 selectivities less than 10%). By comparison with other PIM-1 postmodified membranes from the hydrogens in the spirobisindane moieties, it is not the larger the size of side group is, the more beneficial it is to improve the gas separation performance of PIM-1.