Tailoring the Structure-Property Relationship of Ring-Opened Metathesis Copolymers for CO2-Selective Membranes.

In this work, we explore the use of ring-opening metathesis polymerization (ROMP) facilitated by a second-generation Grubbs catalyst (G2) for the development of advanced polymer membranes aimed at CO2 separation. By employing a novel copolymer blend incorporating 4,4'-oxidianiline (ODA), 1,6-hexanediamine (HDA), 1-adamantylamine (AA), and 3,6,9-trioxaundecylamine (TA), along with a CO2-selective poly(ethylene glycol)/poly(propylene glycol) copolymer (Jeffamine2003) and polydimethylsiloxane (PDMS) units, we have synthesized membranes under ambient conditions with exceptional CO2 separation capabilities. The strategic inclusion of PDMS, up to a 20% composition within the PEG/PPG matrix, has resulted in copolymer membranes that not only surpass the 2008 upper limit for CO2/N2 separation but also meet the commercial targets for CO2/H2 separation. Comprehensive analysis reveals that these membranes adhere to the mixing rule and exhibit percolation behavior across the entire range of compositions (0-100%), maintaining robust antiplasticization performance even under pressures up to 20 atm. Our findings underscore the potential of ROMP in creating precisely engineered membranes for efficient CO2 separation, paving the way for their application in large-scale environmental and industrial processes.

PolyMOF nanoparticles constructed from intrinsically microporous polymer ligand towards scalable composite membranes for CO2 separation.

Integrating different modification strategies into a single step to achieve the desired properties of metal-organic frameworks (MOFs) has been very synthetically challenging, especially in developing advanced MOF/polymer mixed matrix membranes (MMMs). Herein, we report a polymer-MOF (polyMOF) system constructed from a carboxylated polymer with intrinsic microporosity (cPIM-1) ligand. This intrinsically microporous ligand could coordinate with metals, leading to ~100 nm-sized polyMOF nanoparticles. Compared to control MOFs, these polyMOFs exhibit enhanced ultramicroporosity for efficient molecular sieving, and they have better dispersion properties in casting solutions to prepare MMMs. Ultimately, integrating coordination chemistries through the cPIM-1 and polymer-based functionality into porous materials results in polyMOF/PIM-1 MMMs that display excellent CO2 separation performance (surpassing the CO2/N2 and CO2/CH4 upper bounds). In addition to exploring the physicochemical and transport properties of this polyMOF system, scalability has been demonstrated by converting the developed MMM material into large-area (400 cm2) thin-film nanocomposite (TFN) membranes.

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.

In Situ Derived Hybrid Carbon Molecular Sieve Membranes with Tailored Ultramicroporosity for Efficient Gas Separation.

Fine control of ultramicroporosity (<7 Å) in carbon molecular sieve (CMS) membranes is highly desirable for challenging gas separation processes. Here, a versatile approach is proposed to fabricate hybrid CMS (HCMS) membranes with unique textural properties as well as tunable ultramicroporosity. The HCMS membranes are formed by pyrolysis of a polymer nanocomposite precursor containing metal-organic frameworks (MOFs) as a carbonizable nanoporous filler. The MOF-derived carbonaceous phase displays good compatibility with the polymer-derived carbon matrix due to the homogeneity of the two carbon phases, substantially enhancing the mechanical robustness of the resultant HCMS membranes. Detailed structural analyses reveal that the in situ pyrolysis of embedded MOFs induces more densified and interconnected carbon structures in HCMS membranes compared to those in conventional CMS membranes, leading to bimodal and narrow pore size distributions in the ultramicroporous region. Eventually, the HCMS membranes exhibit far superior gas separation performances with a strong size-sieving ability than the conventional polymers and CMS membranes, especially for closely sized gas pairs (Δd < 0.5 Å) including CO2 /CH4 and C3 H6 /C3 H8 separations. More importantly, the developed HCMS material is successfully prepared into a thin-film composite (TFC) membrane (≈1 µm), demonstrating its practical feasibility for use in industrial mixed-gas operation conditions.