Locating the binding domains in a highly selective mixed matrix membrane via synchrotron IR microspectroscopy.

The binding domains within a mixed matrix membrane (MMM) that is selective for CO2 comprising MFM-300(Al) and the polymer 6FDA-Durene-DABA have been established via in situ synchrotron IR microspectroscopy. The MOF crystals are fully accessible and play a critical role in the binding of CO2, creating a selective pathway to promote permeation of CO2 within and through the MMM. This study reveals directly the molecular mechanism for the overall enhanced performance of this MMM in terms of permeability, solubility and selectivity for CO2.

Stepwise observation and quantification and mixed matrix membrane separation of CO2 within a hydroxy-decorated porous host.

The identification of preferred binding domains within a host structure provides important insights into the function of materials. State-of-the-art reports mostly focus on crystallographic studies of empty and single component guest-loaded host structures to determine the location of guests. However, measurements of material properties (e.g., adsorption and breakthrough of substrates) are usually performed for a wide range of pressure (guest coverage) and/or using multi-component gas mixtures. Here we report the development of a multifunctional gas dosing system for use in X-ray powder diffraction studies on Beamline I11 at Diamond Light Source. This facility is fully automated and enables in situ crystallographic studies of host structures under (i) unlimited target gas loadings and (ii) loading of multi-component gas mixtures. A proof-of-concept study was conducted on a hydroxyl-decorated porous material MFM-300(VIII) under (i) five different CO2 pressures covering the isotherm range and (ii) the loading of equimolar mixtures of CO2/N2. The study has successfully captured the structural dynamics underpinning CO2 uptake as a function of surface coverage. Moreover, MFM-300(VIII) was incorporated in a mixed matrix membrane (MMM) with PIM-1 in order to evaluate the CO2/N2 separation potential of this material. Gas permeation measurements on the MMM show a great improvement over the bare PIM-1 polymer for CO2/N2 separation based on the ideal selectivity.

Effect of the porosity of a polymer of intrinsic microporosity (PIM) on its intrinsic fluorescence.

The photophysical properties of a polymer of intrinsic microporosity, namely, PIM-1, were characterized by steady-state and time-resolved fluorescence for solutions of PIM-1 in dichloromethane (DCM) or for a membrane made of PIM-1 immersed in hexane to which a quencher was added. Quenching of PIM-1 by the proton-donor trifluoroacetic acid (TFA), electron-rich tributylamine (TBA), and electron-poor nitromethane (CH3NO2) was investigated and compared to those of the structural unit of PIM-1, the model compound M-1. Only TBA and TFA appeared to quench PIM-1 effectively. The sensitivity of monomer M-1 to the nature of the solvent led us to investigate how addition of a quencher would affect the fluorescence of the polymer PIM-1. Solvent effects were observed for TFA only and were carefully characterized. In particular, it was determined that these solvent effects could be neglected for TFA concentrations smaller than 1.4 mM. Quenching of PIM-1 by TBA was diffusional in nature and occurred in a similar manner for M-1 and PIM-1 in DCM, suggesting that M-1 is locally excited in PIM-1. All M-1 units were accessible and quenched effectively by TBA for PIM-1 in DCM and the PIM-1 membrane in hexane. Quenching of PIM-1 in DCM and in the membrane was more complex, showing a combination of static, diffusive, and protective quenching. The fraction of accessible M-1 units to TFA (f(a)) was determined to be equal to 0.5 for PIM-1 in DCM or in the membrane. The TBA and TFA quenching experiments led to the conclusion that the same accessibility was obtained for the fluorescent constituting units of PIM-1 dissolved in DCM or in a membrane immersed in hexane, in agreement with the known high microporosity of this polymer.

Hexaphenylbenzene-based polymers of intrinsic microporosity.

Microporous polymers derived from the 1,2- and 1,4-regioisomers of di(3',4'-dihydroxyphenyl)tetraphenylbenzene have very different properties with the former being composed predominantly of cyclic oligomers whereas the latter is of high molar mass suitable for the formation of robust solvent-cast films of high gas permeability.

High-performance membranes from polyimides with intrinsic microporosity.

Membranes with high permeability to gases are formed from polyimides with rigid backbones that incorporate a spiro-centre. A route to this new range of high-free-volume polyimides is demonstrated, and exceptional performance is obtained for a polymer containing a dimethyl binaphthyl unit.

Polymers of intrinsic microporosity (PIMs): bridging the void between microporous and polymeric materials.

Novel types of microporous material are required for chemoselective adsorptions, separations and heterogeneous catalysis. This concept article describes recent research directed towards the synthesis of polymeric materials that possess microporosity that is intrinsic to their molecular structures. These polymers (PIMs) can exhibit analogous behaviour to that of conventional microporous materials, but, in addition, may be processed into convenient forms for use as membranes. The excellent performance of these membranes for gas separation and pervaporation illustrates the unique character of PIMs and suggests immediate technological applications.