Plasticization-Resistant Carboxyl-Functionalized 6FDA-Polyimide of Intrinsic Microporosity (PIM–PI) for Membrane-Based Gas Separation

Abstract

A novel trimethyl-substituted carboxyl-containing polyimide was synthesized by a one-pot high temperature polycondensation reaction of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,5-diamino-2,4,6-trimethylbenzoic acid (TrMCA). The polyimide (6FDA-TrMCA) displayed Brunauer-Emmett-Teller (BET) surface area of 260 m 2 g-1 demonstrating intrinsic microporosity in contrast to the related low-free volume COOH-functionalized polyimide 6FDA-DABA. Compared to the non-functionalized 6FDA polyimide analog made from 2,4,6-trimethyl-m-phenylenediamine (TrMPD)also known as 6FDA-DAM-carboxyl functionalization in 6FDA-TrMCA resulted in reduced surface area, lower fractional free volume, and tighter average chain spacing. Gas permeabilities of 6FDA-TrMCA were typical of functionalized polyimides of intrinsic microporosity (PIM-PIs). For example, at 2 atm and 35 °C, 6FDA-TrMCA showed pure-gas H 2 and CO 2 permeability of 193 and 144 barrer coupled with H 2 /CH 4 and CO 2 /CH 4 selectivity of 61 and 45, respectively. Notably, in mixed-gas permeation tests with an equimolar CO 2-CH 4 mixture at 12 atm CO 2 partial pressure, 6FDA-TrMCA demonstrated performance located on the 2018 mixed-gas upper bound with a CO 2 permeability of ~ 98 barrer and CO 2 /CH 4 permselectivity of 38. As the first reported COOH-functionalized PIM-PI homopolymer, 6FDA-TrMCA revealed excellent resistance against CO 2-induced plasticization at least up to a CO 2 partial pressure of 15 atm covering the range of typical wellhead CO 2 partial pressures (5-10 atm).

Molecularly Engineered 6FDA‐Based Polyimide Membranes for Sour Natural Gas Separation

“…As expected, the T g of 6FDA-DAM:DABApolyimide determined by DSC show an obvious increase from 357 8 8Ct o3 75 8 8Ca st he DAM:DABA Angewandte ratio increases from 1:2t o3:2 (Figure 1b,d), indicating that incorporating more DAMmoiety in the polyimide backbone increases the polyimide chain rigidity.T his is due to the presence of bulky methyl groups in DAMmoiety that inhibit localized, rotational mobilities of polymer backbone.S uch rigid backbones of 6FDA-DAM:DABAp olyimides with more DAMm oieties lead to higher packing resistance and suppresses the polymer chain packing in the formed membranes,thus leading to high free volume within the membrane matrix. [12] In addition, previous work [13] demonstrated that carboxyl groups in polyimide can form hydrogen bonds with the carbonyl and imide groups of adjacent polyimide chains. In this case,i tc an tighten chain packing and reduce free volume of the membrane when more DABA is incorporated in the polymer backbone.W ide angle X-ray diffraction (WAXD) measurements were performed and d-spacings of 6FDA-DAM:DABAp olyimide membranes,w hich can be used as an indicator of polymer chain packing in dense films, were calculated using Braggsl aw.R esults represented in Figure 1c Thed-spacings of 6FDA-DAM and 6FDA-DABAp olyimides reported in previous study [14] are shown here for comparison.…”

Hierarchically porous electrospun nanofibrous mats produced from intrinsically microporous fluorinated polyimide for the removal of oils and non-polar solvents

“…The fluorinated porous polyimide polymer was synthesized by reacting 6FDA (0.59 g, 1.33 mmol) with TrMPD (0.2 g, 1.33 mmol) in m-cresol (3 mL) in a 25 mL Schlenk tube equipped with a mechanical stirrer, a nitrogen inlet and an oil bubbler (Scheme 1). 27 The solution was heated to 80°C and isoquinoline (0.1 mL) was added under nitrogen, followed by stirring at 200°C for 4 h. Dry nitrogen stream was used to remove water, which resulted from the conversion of polyamic acid to polyimide. The viscous solution was cooled and poured into methanol, resulting in the precipitation of the polymer in a fibrous form, which was collected by filtration and purified twice by re-precipitation from solutions of N,N-dimethylformamide (DMF) into methanol.…”

A radical polymer for highly efficient solar evaporation and gas separation

“…36,37 Thus, RP-COOH shows higher CO2 sorption over the full range of pressure than RP-CN (Figure 4d), enhancing the permeability of the RP-COOH membrane. The slight drop of H2 permeability maybe contributed by the lower fractional free volume and tighter average chain spacing after carboxyl functionalization in RP-COOH, 39 evidenced by PALS study (Figure 4e).…”