Highly Carboxylate-Functionalized Polymers of Intrinsic Microporosity for CO₂-Selective Polymer Membranes

Abstract

Carboxylate-functionalized polymers of intrinsic microporosity (PIMs) are promising materials for gas separation application. However, highly carboxylate-functionalized PIMs (HCPIMs) have not been reported owing to overlooked intermediate products. Herein, we successfully prepared HCPIMs (∼92 mol % of carboxylic acid group) through a prolonged alkaline hydrolysis process (360 h). HCPIMs were found to be soluble in various organic solvents, such as tetrahydrofuran and dimethyl sulfoxide, and then free-standing HCPIM membranes could be prepared by the common solution casting method. The HCPIM membranes were found to have smaller interchain distances and higher CO2 affinity than original PIM-1 films. For example, small gas molecules, such as carbon dioxide, were effectively separated due to the enhanced diffusivity selectivity combined with the smaller cavity size. Further, strong interactions between carbon dioxide and the carboxylic acid groups increased solubility selectivity. These synergetic effects endowed the HCPIM membrane with a selectivity of 53.6 for CO2/N2 separation, the highest among reported chemically modified PIMs.

Effective Conversion of Amide to Carboxylic Acid on Polymers of Intrinsic Microporosity (PIM-1) with Nitrous Acid

“…Most recently, Jeon et al successfully obtained a fully converted C-PIM (>92 mol % COOH content) after an exhaustive 360 h (15 days) base-hydrolysis [ 34 ]. The resulting C-PIM film exhibited outstanding selectivity of 53.6 for CO 2 /N 2 gas pair [ 34 ]. However, this extremely slow reaction rate is not ideal and could be a barrier to large scale industrial implementation.…”

Carbonization of Carboxylate‐Functionalized Polymers of Intrinsic Microporosity for Water Treatment

“…Figure S1a (Supporting Information) shows that PIM‐COOH have a ladder–type structure with a dibenzodioxin linkage, a spiro‐center, and carboxylic acid functional groups 22. Figure S1b (Supporting Information) shows that these structural units cause microporosity owing to the inefficient packing of the polymer chains 15.…”

“…For the analysis of intra‐ and intermolecular distances of PIM‐COOH, the average interchain distances ( d ‐spacing) were confirmed by XRD and determined by Bragg's law ( d = λ/(2 sin θ)). The pristine PIM‐COOH samples have three major peaks, attributed to the chain‐to‐chain distance of aromatic systems (3.93 Å), efficiently arranged polymer chain (4.80 Å), and loosely packed polymer chains (6.01 Å) 22,31. After thermal decarboxylation (Stage 2), these peaks still remained; however, they shifted to lower angles for both the efficiently arranged polymer chain (4.95 Å) and loosely packed polymer chains (6.16 Å), indicating that chain‐to‐chain distances were broadened owing to the loss of hydrogen bonds between the carboxylic acids and the evolution of CO 2 gases.…”

“…The EA results are summarized in Figure and Table S1 (Supporting Information). The prepared four samples mostly comprised carbon, hydrogen, and oxygen 22. Comparing the experimental and expected values, the experimental values of both PIM‐COOH (Stage 1) and cPIM‐COOH 350 (Stage 2) were in accordance with the theoretical ones.…”

Hydrophilic Microporous Polymer Membranes: Synthesis and Applications

“…As À NH 2 is a poor leaving group, harsher reaction conditions or longer reaction time are needed to promote the conversion of the intermediate amides to carboxylic acids. Jeon et al prepared a highly carboxylatefunctionalized PIM-1 (around 92 mol % of carboxylic acids) by further extending the reaction time to 360 h. [17] COOH-PM-1 is hydrophilic due to the introduction of carboxylic groups. It's worth mentioning that the hydrophilicity can be further increased by alkali treatment that converts the À COOH groups to À COO À salt.…”