Poly(vinyl chloride) Dechlorination Catalyzed by Zirconium.

Poly(vinyl chloride) undergoes dechlorination in the presence of triethylsilane (Et3SiH) and a catalytic amount of [Cp2Zr(NPh2)][CH3B(C6F5)3] (1 b) at 40-80 °C, with up to 91 % efficiency. Stoichiometric reactivity studies conducted on cyclohexyl chloride as a model suggest that 1 b dechlorinates PVC by initial chloride abstraction, followed by hydride transfer to the cationic PVC chain from Et3SiH. Consumer items such as pipe fitting, vinyl disc or electric cable insulation undergo either dechlorination or hydrosilylation of the carbonyl-containing copolymer (polyvinyl acetate) or plasticizer (phthalate).

Tröger's Base Network Polymers of Intrinsic Microporosity (TB-PIMs) with Tunable Pore Size for Heterogeneous Catalysis.

Heterogeneous catalysis plays a pivotal role in the preparation of value-added chemicals, and it works more efficiently when combined with porous materials and supports. Because of that, a detailed assessment of porosity and pore size is essential when evaluating the performance of new heterogeneous catalysts. Herein, we report the synthesis and characterization of a series of novel microporous Tröger's base polymers and copolymers (TB-PIMs) with tunable pore size. The basicity of TB sites is exploited to catalyze the Knoevenagel condensation of benzaldehydes and malononitrile, and the dimension of the pores can be systematically adjusted with an appropriate selection of monomers and comonomers. The tunability of the pore size provides the enhanced accessibility of the catalytic sites for substrates, which leads to a great improvement in conversions, with the best results achieving completion in only 20 min. In addition, it enables the use of large benzaldehydes, which is prevented when using polymers with very small pores, typical of conventional PIMs. The catalytic reaction is more efficient than the corresponding homogeneous counterpart and is ultimately optimized with the addition of a small amount of a solvent, which facilitates the swelling of the pores and leads to a further improvement in the performance and to a better carbon economy. Molecular dynamic modeling of the copolymers' structures is employed to describe the swellability of flexible chains, helping the understanding of the improved performance and demonstrating the great potential of these novel materials.

CO2 Separation by Imide/Imine Organic Cages.

Invited for the cover of this issue are the groups of Valeria Amendola at the University of Pavia, Mariolino Carta at the University of Swansea, and Johannes C. Jansen at the CNR-ITM. The image depicts one of the novel imide/imine organic cages that were employed as fillers in mixed-matrix membranes for the selective separation of CO2 from N2 and CH4 . Read the full text of the article at 10.1002/chem.202201631.

CO2 Separation by Imide/Imine Organic Cages.

Two novel imide/imine-based organic cages have been prepared and studied as materials for the selective separation of CO2 from N2 and CH4 under vacuum swing adsorption conditions. Gas adsorption on the new compounds showed selectivity for CO2 over N2 and CH4 . The cages were also tested as fillers in mixed-matrix membranes for gas separation. Dense and robust membranes were obtained by loading the cages in either Matrimid® or PEEK-WC polymers. Improved gas-transport properties and selectivity for CO2 were achieved compared to the neat polymer membranes.

Polymers of Intrinsic Microporosity in the Design of Electrochemical Multicomponent and Multiphase Interfaces.

Polymers of intrinsic microporosity (or PIMs) provide porous materials due to their highly contorted and rigid macromolecular structures, which prevent space-efficient packing. PIMs are readily dissolved in solvents and can be cast into robust microporous coatings and membranes. With a typical micropore size range of around 1 nm and a typical surface area of 700-1000 m2 g-1, PIMs offer channels for ion/molecular transport and pores for gaseous species, solids, and liquids to coexist. Electrode surfaces are readily modified with coatings or composite films to provide interfaces for solid|solid|liquid or solid|liquid|liquid or solid|liquid|gas multiphase electrode processes.

BN-Doped Metal-Organic Frameworks: Tailoring 2D and 3D Porous Architectures through Molecular Editing of Borazines.

Building on the MOF approach to prepare porous materials, herein we report the engineering of porous BN-doped materials using tricarboxylic hexaarylborazine ligands, which are laterally decorated with functional groups at the full-carbon 'inner shell'. Whilst an open porous 3D entangled structure could be obtained from the double interpenetration of two identical metal frameworks derived from the methyl substituted borazine, the chlorine-functionalised linker undergoes formation of a porous layered 2D honeycomb structure, as shown by single-crystal X-ray diffraction analysis. In this architecture, the borazine cores are rotated by 60° in alternating layers, thus generating large rhombohedral channels running perpendicular to the planes of the networks. An analogous unsubstituted full-carbon metal framework was synthesised for comparison. The resulting MOF revealed a crystalline 3D entangled porous structure, composed by three mutually interpenetrating networks, hence denser than those obtained from the borazine linkers. Their microporosity and CO2 uptake were investigated, with the porous 3D BN-MOF entangled structure exhibiting a large apparent BET specific surface area (1091 m2 g-1 ) and significant CO2 reversible adsorption (3.31 mmol g-1 ) at 1 bar and 273 K.

Intrinsically Microporous Polymer Nanosheets for High-Performance Gas Separation Membranes.

Microporous polymer nanosheets with thicknesses in the range 3-5 nm and with high apparent surface area (Brunauer-Emmett-Teller surface area 940 m2 g-1 ) are formed when the effectively bifunctional (tetrafluoro) monomer used in the preparation of the prototypical polymer of intrinsic microporosity PIM-1 is replaced with an effectively tetrafunctional (octafluoro) monomer to give a tightly crosslinked network structure. When employed as a filler in mixed-matrix membranes based on PIM-1, a low loading of 0.5 wt% network-PIM-1 nanosheets gives rise to enhanced CO2 permeability and CO2 /CH4 selectivity, compared to pure PIM-1.

Polymer ultrapermeability from the inefficient packing of 2D chains.

The promise of ultrapermeable polymers, such as poly(trimethylsilylpropyne) (PTMSP), for reducing the size and increasing the efficiency of membranes for gas separations remains unfulfilled due to their poor selectivity. We report an ultrapermeable polymer of intrinsic microporosity (PIM-TMN-Trip) that is substantially more selective than PTMSP. From molecular simulations and experimental measurement we find that the inefficient packing of the two-dimensional (2D) chains of PIM-TMN-Trip generates a high concentration of both small (<0.7 nm) and large (0.7-1.0 nm) micropores, the former enhancing selectivity and the latter permeability. Gas permeability data for PIM-TMN-Trip surpass the 2008 Robeson upper bounds for O2/N2, H2/N2, CO2/N2, H2/CH4 and CO2/CH4, with the potential for biogas purification and carbon capture demonstrated for relevant gas mixtures. Comparisons between PIM-TMN-Trip and structurally similar polymers with three-dimensional (3D) contorted chains confirm that its additional intrinsic microporosity is generated from the awkward packing of its 2D polymer chains in a 3D amorphous solid. This strategy of shape-directed packing of chains of microporous polymers may be applied to other rigid polymers for gas separations.

Towards High Performance Metal-Organic Framework-Microporous Polymer Mixed Matrix Membranes: Addressing Compatibility and Limiting Aging by Polymer Doping.

Membrane separation for gas purification is an energy-efficient and environment-friendly technology. However, the development of high performance membranes is still a great challenge. In principle, mixed matrix membranes (MMMs) have the potential to overcome current materials limitations, but in practice there is no straightforward method to match the properties of fillers and polymers (the main components of MMMs) in such a way that the final membrane performance reflects the high performance of the microporous filler and the processability of the continuous polymer phase. This issue is especially important when high flux polymers are utilized. In this work, we demonstrate that the use of small amounts of a glassy polymer in combination with high performance PIM-1 allow for the preparation of metal-organic framework (MOF)-based MMMs with superior separation properties and low aging rates under humid conditions, meeting the commercial target for post-combustion CO2 capture.

The Synthesis of Organic Molecules of Intrinsic Microporosity Designed to Frustrate Efficient Molecular Packing.

Efficient reactions between fluorine-functionalised biphenyl and terphenyl derivatives with catechol-functionalised terminal groups provide a route to large, discrete organic molecules of intrinsic microporosity (OMIMs) that provide porous solids solely by their inefficient packing. By altering the size and substituent bulk of the terminal groups, a number of soluble compounds with apparent BET surface areas in excess of 600 m(2) g(-1) are produced. The efficiency of OMIM structural units for generating microporosity is in the order: propellane>triptycene>hexaphenylbenzene>spirobifluorene>naphthyl=phenyl. The introduction of bulky hydrocarbon substituents significantly enhances microporosity by further reducing packing efficiency. These results are consistent with findings from previously reported packing simulation studies. The introduction of methyl groups at the bridgehead position of triptycene units reduces intrinsic microporosity. This is presumably due to their internal position within the OMIM structure so that they occupy space, but unlike peripheral substituents they do not contribute to the generation of free volume by inefficient packing.

Highly Conductive Anion-Exchange Membranes from Microporous Tröger's Base Polymers.

The development of polymeric anion-exchange membranes (AEMs) combining high ion conductivity and long-term stability is a major challenge for materials chemistry. AEMs with regularly distributed fixed cationic groups, based on the formation of microporous polymers containing the V-shape rigid Tröger's base units, are reported for the first time. Despite their simple preparation, which involves only two synthetic steps using commercially available precursors, the polymers provide AEMs with exceptional hydroxide conductivity at relatively low ion-exchange capacity, as well as a high swelling resistance and chemical stability. An unprecedented hydroxide conductivity of 164.4 mS cm(-1) is obtained at a relatively a low ion-exchange capacity of 0.82 mmol g(-1) under optimal operating conditions. The exceptional anion conductivity appears related to the intrinsic microporosity of the charged polymer matrix, which facilitates rapid anion transport.

Intrinsically Microporous Polymer Retains Porosity in Vacuum Thermolysis to Electroactive Heterocarbon.

Vacuum carbonization of organic precursors usually causes considerable structural damage and collapse of morphological features. However, for a polymer with intrinsic microporosity (PIM-EA-TB with a Brunauer-Emmet-Teller (BET) surface area of 1027 m(2)g(-1)), it is shown here that the rigidity of the molecular backbone is retained even during 500 °C vacuum carbonization, yielding a novel type of microporous heterocarbon (either as powder or as thin film membrane) with properties between those of a conducting polymer and those of a carbon. After carbonization, the scanning electron microscopy (SEM) morphology and the small-angle X-ray scattering (SAXS) Guinier radius remain largely unchanged as does the cumulative pore volume. However, the BET surface area is decreased to 242 m(2)g(-1), but microporosity is considerably increased. The new material is shown to exhibit noticeable electrochemical features including two pH-dependent capacitance domains switching from ca. 33 Fg(-1) (when oxidized) to ca. 147 Fg(-1) (when reduced), a low electron transfer reactivity toward oxygen and hydrogen peroxide, and a four-point-probe resistivity (dry) of approximately 40 MΩ/square for a 1-2 µm thick film.

Metastable ionic diodes derived from an amine-based polymer of intrinsic microporosity.

A highly rigid amine-based polymer of intrinsic microporosity (PIM), prepared by a polymerization reaction involving the formation of Tröger's base, is demonstrated to act as an ionic diode with electrolyte-dependent bistable switchable states.

Triphasic Oxygen Storage in Wet Nanoparticulate Polymer of Intrinsic Microporosity (PIM-1) on Platinum: An Electrochemical Investigation.

The triphasic interaction of gases with electrode surfaces immersed in aqueous electrolyte is crucial in electrochemical technologies (fuel cells, batteries, sensors). Some microporous materials modify this interaction locally via triphasic storage capacity for gases in aqueous environments linked to changes in apparent oxygen concentration and diffusivity (as well as activity and reactivity). Here, a nanoparticulate polymer of intrinsic microporosity (PIM-1) in aqueous electrolyte is shown to store oxygen gas and thereby enhance electrochemical signals for oxygen reduction in aqueous media. Oxygen reduction current transient data at platinum disk electrodes suggest that the reactivity of ambient oxygen in aqueous electrolyte (typically Doxygen = 2.8 × 10-9 m2 s-1; coxygen = 0.3 mM) is substantially modified (to approximately Dapp,oxygen = 1.6 (±0.3) × 10-12 m2 s-1; capp,oxygen = 50 (±5) mM) with important implications for triphasic electrode processes. The considerable apparent concentration of oxygen even for ambient oxygen levels is important. Potential applications in oxygen sensing, oxygen storage, oxygen catalysis, or applications associated with other types of gases are discussed.

Hydrophobic assembly of molecular catalysts at the gas-liquid-solid interface drives highly selective CO2 electromethanation.

Molecular catalysts offer tunable active and peripheral sites, rendering them ideal model systems to explore fundamental concepts in catalysis. However, hydrophobic designs are often regarded as detrimental for dissolution in aqueous electrolytes. Here we show that established cobalt terpyridine catalysts modified with hydrophobic perfluorinated alkyl side chains can assemble at the gas-liquid-solid interfaces on a gas diffusion electrode. We find that the self-assembly of these perfluorinated units on the electrode surface results in a catalytic system selective for electrochemical CO2 reduction to CH4, whereas every other cobalt terpyridine catalyst reported previously was only selective for CO or formate. Mechanistic investigations suggest that the pyridine units function as proton shuttles that deliver protons to the dynamic hydrophobic pocket in which CO2 reduction takes place. Finally, integration with fluorinated carbon nanotubes as a hydrophobic conductive scaffold leads to a Faradaic efficiency for CH4 production above 80% at rates above 10 mA cm-2-impressive activities for a molecular electrocatalytic system.

The Difference in Performance and Compatibility between Crystalline and Amorphous Fillers in Mixed Matrix Membranes for Gas Separation (MMMs).

An increasing number of high-performing gas separation membranes is reported almost on a daily basis, yet only a few of them have reached commercialisation while the rest are still considered pure research outcomes. This is often attributable to a rapid change in the performance of these separation systems over a relatively short time. A common approach to address this issue is the development of mixed matrix membranes (MMMs). These hybrid systems typically utilise either crystalline or amorphous additives, so-called fillers, which are incorporated into polymeric membranes at different loadings, with the aim to improve and stabilise the final gas separation performance. After a general introduction to the most relevant models to describe the transport properties in MMMs, this review intends to investigate and discuss the main advantages and disadvantages derived from the inclusion of fillers of different morphologies. Particular emphasis will be given to the study of the compatibility at the interface between the filler and the matrix created by the two different classes of additives, the inorganic and crystalline fillers vs. their organic and amorphous counterparts. It will conclude with a brief summary of the main findings.

Tuning and Coupling Irreversible Electroosmotic Water Flow in Ionic Diodes: Methylation of an Intrinsically Microporous Polyamine (PIM-EA-TB).

Molecularly rigid polymers with internal charges (positive charges induced by amine methylation) allow electroosmotic water flow to be tuned by adjusting the charge density (the degree of methylation). Here, a microporous polyamine (PIM-EA-TB) is methylated to give a molecularly rigid anion conductor. The electroosmotic drag coefficient (the number of water molecules transported per anion) is shown to increase with a lower degree of methylation. Net water transport (without charge flow) in a coupled anionic diode circuit is demonstrated based on combining low and high electroosmotic drag coefficient materials. The AC-electricity-driven net process offers water transport (or transport of other neutral species, e.g., drugs) with net zero ion transport and without driver electrode side reactions.

Nanophase-photocatalysis: loading, storing, and release of H2O2 using graphitic carbon nitride.

A blue light mediated photochemical process using solid graphitic carbon nitride (g-C3N4) in ambient air/isopropanol vapour is suggested to be linked to "nanophase" water inclusions and is shown to produce approx. 50 µmol H2O2 per gram of g-C3N4, which can be stored in the solid g-C3N4 for later release for applications, for example, in disinfection or anti-bacterial surfaces.

Adjustable Functionalization of Hyper-Cross-Linked Polymers of Intrinsic Microporosity for Enhanced CO2 Adsorption and Selectivity over N2 and CH4.

In this paper, we report the design, synthesis, and characterization of a series of hyper-cross-linked polymers of intrinsic microporosity (PIMs), with high CO2 uptake and good CO2/N2 and CO2/CH4 selectivity, which makes them competitive for carbon capture and biogas upgrading. The starting hydrocarbon polymers' backbones were functionalized with groups such as -NO2, -NH2, and -HSO3, with the aim of tuning their adsorption selectivity toward CO2 over nitrogen and methane. This led to a significant improvement in the performance in the potential separation of these gases. All polymers were characterized via Fourier transform infrared (FTIR) spectroscopy and 13C solid-state NMR to confirm their molecular structures and isothermal gas adsorption to assess their porosity, pore size distribution, and selectivity. The insertion of the functional groups resulted in an overall decrease in the porosity of the starting polymers, which was compensated with an improvement in the final CO2 uptake and selectivity over the chosen gases. The best uptakes were achieved with the sulfonated polymers, which reached up to 298 mg g-1 (6.77 mmol g-1), whereas the best CO2/N2 selectivities were recorded by the aminated polymers, which reached 26.5. Regarding CH4, the most interesting selectivities over CO2 were also obtained with the aminated PIMs, with values up to 8.6. The reason for the improvements was ascribed to a synergetic contribution of porosity, choice of the functional group, and optimal isosteric heat of adsorption of the materials.

Effects of g-C3N4 Heterogenization into Intrinsically Microporous Polymers on the Photocatalytic Generation of Hydrogen Peroxide.

Graphitic carbon nitride (g-C3N4) is known to photogenerate hydrogen peroxide in the presence of hole quenchers in aqueous environments. Here, the g-C3N4 photocatalyst is embedded into a host polymer of intrinsic microporosity (PIM-1) to provide recoverable heterogenized photocatalysts without loss of activity. Different types of g-C3N4 (including Pt@g-C3N4, Pd@g-C3N4, and Au@g-C3N4) and different quenchers are investigated. Exploratory experiments yield data that suggest binding of the quencher either (i) directly by adsorption onto the g-C3N4 (as shown for α-glucose) or (ii) indirectly by absorption into the microporous polymer host environment (as shown for Triton X-100) enhances the overall photochemical H2O2 production process. The amphiphilic molecule Triton X-100 is shown to interact only weakly with g-C3N4 but strongly with PIM-1, resulting in accumulation and enhanced H2O2 production due to the microporous polymer host.