Gas separation performance of solid-state in-situ thermally crosslinked 6FDA-based polyimides

Preparation, Thermal Stability, and Preliminary Gas Separation Performance of Furan-Based Bio-Polyimide Films

The need for renewable alternatives to petroleum-based polymers is growing in response to environmental concerns and resource depletion. Polyimides (PIs), which are traditionally synthesized from petroleum-derived monomers, raise sustainability issues. In this work, renewable 2,5-furandicarboxylic acid (FDCA) was employed as a sustainable feedstock to synthesize a bio-based diamine monomer, N,N'-bis(4-aminophenyl)furan-2,5-dicarboxamide (FPA). Subsequently, FPA was polymerized with various aromatic dianhydrides through thermal imidization, yielding four distinct bio-based polyimide (FPA-PI) films. The resulting films exhibited exceptional thermal stability, with 5% weight loss temperatures exceeding 425 °C and char yields ranging from 54% to 60%. Mechanical characterization revealed high elastic moduli (2.14-3.20 GPa), moderate tensile strengths (50-99 MPa), and favorable aging resistance. Gas permeation tests demonstrated promising CO2/N2 separation performance, with FPA-DODDA achieving superior CO2/N2 selectivity (27.721) compared to commercial films such as Matrimid®, polysulfone, and polycarbonate, while FPA-BPFLDA exhibited enhanced CO2 permeability (P(CO2) = 2.526 Barrer), surpassing that of Torlon®. The CO2/N2 separation performance of these FPA-PI films is governed synergistically by size-sieving effects and solution-diffusion mechanisms. This work not only introduces a novel synthetic route for bio-based polymers but also highlights the potential of replacing conventional petroleum-based materials with renewable alternatives in high-temperature and gas separation applications, thereby advancing environmental sustainability.

High-Performance Carbon Capture with Fluorine-Tailored Carbon Molecular Sieve Membranes

Increasing energy consumption and climate change present an urgent global challenge to achieve carbon neutrality, with CO2 capture as a top priority. Among various carbon capture technologies, CO2 membrane separation stands out for its simplicity and energy efficiency in applications including gas purification and industrial gas recovery. Herein, a series of fluorine-tailored porous carbon molecular sieve (CMS) membranes derived from precisely designed precursors, achieving a well-balanced high permeability and selectivity for CO2 separation are developed. Incorporating bent terphenyl monomers and both aliphatic/aromatic trifluoromethyl groups disrupted dense chain packing and promoted pore formation with enhanced permeability and selectivity for CO2 separation. The TFM-550 membrane, derived from a fluorinated stretched polymer backbone precursor, exhibits exceptional performance with a CO2 permeability of 47 190 ± 3204 Barrer and a CO2/N2 selectivity of 28.3 ± 5.7, while TFM-800 presented a higher selectivity of 71.8 ± 11.5, surpassing the 2019 upper bound. Furthermore, under flue gas conditions (CO2/O2/N2 = 1/1/4 in molar ratio), the CMS membrane demonstrate high CO2 permeability of 36,204 ± 2,235 Barrer and outstanding CO2/N2 selectivity of 35.3 ± 1.8. The results here highlight the effectiveness of fluorine tailoring and the potential of fluorinated CMS membranes for sustainable industrial carbon capture applications.

Hydroxyl-Functionalized Polymers of Intrinsic Microporosity and Dual-Functionalized Blends for High-Performance Membrane-Based Gas Separations

Membrane technology has shown significant growth during the past two decades in the gas separation industry due to its energy-savings, compact and modular design, continuous operation, and environmentally benign nature. Robust materials with higher permeability and selectivity are key to reduce capital and operational cost, pushing it forward to replace or debottleneck conventional energy-intensive unit operations such as distillation. Recently designed ladder polymers of intrinsic microporosity (PIM) and polyimides of intrinsic microporosity (PIM-PI) with pores <20 Å have demonstrated excellent gas permeation performance. Here, a series of plasticization-resistant PIM-based membrane materials is reported, including the first example of a hydroxyl-functionalized triptycene- and Tröger's base-derived ladder PIM and two PIM-PI homopolymers and a series of dual-functionalized polyimide blends containing hydroxyl- and carboxyl-functionalized groups. Specifically, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA)-based PIM-PI blends demonstrated extremely high selectivity for a variety of industrially important applications. An optimized polyimide blend containing ─OH and ─COOH groups showed permselectivity values of 136 for CO2/CH4, 11.4 for O2/N2 and 636 for H2/CH4. Such extreme size-sieving capabilities are attributed to physical crosslinking induced by strong hydrogen bonding forming tightly structured polymer networks. The study provides a new general strategy for developing plasticization resistant, robust, and highly-selective PIM-based membrane materials.

Dynamic Covalent Adaptable Polyimide Hybrid Dielectric Films with Superior Recyclability

Polyimides (PIs) used in advanced electrical and electronic devices can be electrically/mechanically damaged, resulting in a significant waste of resources. Closed-loop chemical recycling may prolong the service life of synthetic polymers. However, the design of dynamic covalent bonds for preparing chemically recyclable crosslinked PIs remains a challenging task. Herein, new crosslinked PI films containing a PI oligomer, chain extender, and crosslinker are reported. They exhibit superior recyclability and excellent self-healable ability owing to the synergistic effect of the chain extender and crosslinker. The produced films can be completely depolymerized in an acidic solution at ambient temperature, leading to efficient monomer recovery. The recovered monomers may be used to remanufacture crosslinked PIs without deteriorating their original performance. In particular, the designed films can serve as corona-resistant films with a recovery rate of approximately 100%. Furthermore, carbon fiber reinforced composites (CFRCs) with PI matrices are suitable for harsh environments and can be recycled multiple times at a non-destructive recycling rate up to 100%. The preparation of high-strength dynamic covalent adaptable PI hybrid films from simple PI oligomers, chain extenders, and crosslinkers may provide a solid basis for sustainable development in the electrical and electronic fields.

Tailoring the Micropore Structure of 6FDA-Based Network Polyimide Membranes for Advanced Gas Separation by Decarboxylation

The 6FDA-based network PI has attracted significant attention for gas separation. A facile strategy to tailor the micropore structure within the network PI membrane prepared by the in situ crosslinking method is extremely significant for achieving an advanced gas separation performance. In this work, the 4,4'-diamino-2,2'-biphenyldicarboxylic acid (DCB) or 3,5-diaminobenzoic acid (DABA) comonomer was incorporated into the 6FDA-TAPA network polyimide (PI) precursor via copolymerization. The molar content and the type of carboxylic-functionalized diamine were varied in order to easily tune the resulting network PI precursor structure. Then, these network PIs containing carboxyl groups underwent further decarboxylation crosslinking during the following heat treatment. Properties involving thermal stabilities, solubility, d-spacing, microporosity, and mechanical properties were investigated. Due to the decarboxylation crosslinking, the d-spacing and the BET surface areas of the thermally treated membranes were increased. Moreover, the content of DCB (or DABA) played a key role in determining the overall gas separation performance of the thermally treated membranes. For instance, after the heating treatment at 450 °C, 6FDA-DCB:TAPA (3:2) showed a large increment of about ~532% for CO₂ gas permeability (~266.6 Barrer) coupled with a decent CO₂/N₂ selectivity~23.6. This study demonstrates that incorporating the carboxyl-containing functional unit into the PI backbone to induce decarboxylation offers a practical approach with which to tailor the micropore structure and corresponding gas transport properties of 6FDA-based network PIs prepared by the in situ crosslinking method.

Surface Modification of Matrimid® 5218 Polyimide Membrane with Fluorine-Containing Diamines for Efficient Gas Separation

Polyimide membranes have been widely investigated in gas separation applications due to their high separation abilities, excellent processability, relatively low cost, and stabilities. Unfortunately, it is extremely challenging to simultaneously achieve both improved gas permeability and selectivity due to the trade-off relationship in common polymer membranes. Diamine modification is a simple strategy to tune the separation performance of polyimide membranes, but an excessive loss in permeability is also generally observed. In the present work, we reported the effects of diamine type (i.e., non-fluorinated and fluorinated) on the physicochemical properties and the corresponding separation performance of a modified membrane using a commercial Matrimid® 5218 polyimide. Detailed spectroscopic, thermal, and surface analyses reveal that the bulky fluorine groups are responsible for the balanced chain packing modes in the resulting Matrimid membranes compared to the non-fluorinated diamines. Consequently, the modified Matrimid membranes using fluorinated diamines exhibit both higher gas permeability and selectivity than those of pristine Matrimid, making them especially effective for improving the separation performance towards H2/CH4 and CO2/CH4 pairs. The results indicate that the use of fluorinated modifiers may offer new opportunities to tune the gas transport properties of polyimide membranes.