Polymers of intrinsic microporosity have recently received considerable attention because of their microporosity and solution processability, which extraordinary properties are based on their highly rigid ladder-type and contorted structure. Since PIM-1, a representative polymer of PIMs, was firstly synthesized, novel polymers of intrinsic microporosity with diverse chemical structure have been develop, which lead to a desirable property on specific application such as gas separation. Especially, introduction of new functionality such as carboxylic acid, amine, and thioamide alter their chemical and physical characteristics of the membrane. Among those functionalization of PIMs, carboxylation of PIM-1 are regarded as promising postmodification. However, highly carboxylate-functionalized PIMs (HCPIMs) have not been reported yet owing to overlooked intermediates, such as amide. In this study, we successfully prepared HCPIMs (~92 mol% of carboxylic acid group) through a prolonged alkaline hydrolysis reaction (360 h). The conversion of PIM-1 to PIM-COOH was thoroughly recorded by FT-IR, elemental analysis (EA), and 1H NMR spectroscopy. Also, we found that HCPIMs were soluble in various organic solvents, such as tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO), and then free-standing HCPIM membranes was prepared by solution casting method. Through XRD and CO2 adsorption experiment, the HCPIM membranes were found to have smaller cavity size and higher CO2 affinity than original PIM-1 films. Due to chemical and physical changes through alkaline hydrolysis, HCPIM membranes effectively filtered out small gas molecules, such as carbon dioxide, because of the enhanced diffusivity selectivity combined with the smaller cavity size. Specifically, enhanced solubility selectivity can be attributed to strong Lewis acid-base interactions or hydrogen bonding and electrostatic interaction between carbon dioxide and the carboxylic acid groups. These synergetic effects endowed the HCPIM membrane with a superior selectivity of 53 for CO2/N2 separation, the highest among reported chemically modified PIMs.

Highly carboxylate-functionalized polymers of intrinsic microporosity for superior CO2 selective gas separation membrane

256th National Meeting (2018)

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