Mariolino Carta

An Efficient Polymer Molecular Sieve for Membrane Gas Separations

Bicyclic Bridge to Improvement Polymers of intrinsic microporosity are a recently developed class of contorted rigid glassy ladderlike polymers having very high free volume (open internal spaces). The intrinsic porosity of these materials has made them of interest for ultrahigh permeability gas separation membranes. However, while the polymers show good gas permeability, they have only moderate gas selectivity. Carta et al. (p. 303; see the Perspective by Guiver and Lee) hypothesized that if they could replace the dioxin-like rings in their polymers with stiffer bridged bicyclic rings, they could improve the membrane properties of the polymer. By exploiting reactions connected to the formation of Trögers base to form the multiple covalent bonds needed to make the bicyclic rings, the resulting polymers showed significantly improved selectivity and permeability. Intrinsically porous polymers made using reactions associated with Tröger’s base manifested enhanced membrane properties. [Also see Perspective by Guiver and Lee] Microporous polymers of extreme rigidity are required for gas-separation membranes that combine high permeability with selectivity. We report a shape-persistent ladder polymer consisting of benzene rings fused together by inflexible bridged bicyclic units. The polymer’s contorted shape ensures both microporosity—with an internal surface area greater than 1000 square meters per gram—and solubility so that it is readily cast from solution into robust films. These films demonstrate exceptional performance as molecular sieves with high gas permeabilities and good selectivities for smaller gas molecules, such as hydrogen and oxygen, over larger molecules, such as nitrogen and methane. Hence, this polymer has excellent potential for making membranes suitable for large-scale gas separations of commercial and environmental relevance.

A Spirobifluorene‐Based Polymer of Intrinsic Microporosity with Improved Performance for Gas Separation

A highly gas-permeable polymer with enhanced selectivities is prepared using spirobifluorene as the main structural unit. The greater rigidity of this polymer of intrinsic microporosity (PIM-SBF) facilitates gas permeability data that lie above the 2008 Robeson upper bound, which is the universal performance indicator for polymer gas separation membranes.

Triptycene Induced Enhancement of Membrane Gas Selectivity for Microporous Tröger's Base Polymers

A highly gas permeable polymer with exceptional size selectivity is prepared by fusing triptycene units together via a poly-merization reaction involving Trögers base formation. The extreme rigidity of this polymer of intrinsic microporosity (PIM-Trip-TB) facilitates gas permeability data that lie well above the benchmark 2008 Robeson upper bounds for the important O2 /N2 and H2 /N2 gas pairs.

A highly permeable polyimide with enhanced selectivity for membrane gas separations

A highly gas permeable polyimide with improved molecular sieving properties is produced by using a bisanhydride monomer based on the rigid ethanoanthracene unit. The polymer (PIM-PI-EA) demonstrates enhanced selectivity for gas separations so that its gas permeability data lie above the 2008 Robeson upper bounds for the important O2–N2, H2–N2, CO2–CH4 and CO2–N2 gas pairs.

Novel spirobisindanes for use as precursors to polymers of intrinsic microporosity

The synthesis of novel spirobisindane-based monomers for the preparation of polymers of intrinsic microporosity (PIMs) with bulky, rigid substituents is described. Polymers derived from monomers containing spiro-linked fluorene substituents display enhanced solubility and microporosity due to additional frustration of packing in the solid state.

The synthesis of microporous polymers using Tröger's base formation

A step-growth polymerisation based on the formation of Trogers base, performed by simple reaction of a suitable aromatic diamine monomer with dimethoxymethane in trifluoroacetic acid, provides polymers of high average molecular mass. The properties of the resulting polymers can be tailored by the choice of monomer. In particular, the Trogers base polymerisation is highly suited to the preparation of soluble polymers of intrinsic microporosity (PIMs) due to the resulting fused-ring TB linking group, which is both highly rigid and prohibits conformational freedom.

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 Trögers 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.

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 Trögers base, is demonstrated to act as an ionic diode with electrolyte-dependent bistable switchable states.

Synthesis of cardo-polymers using Tröger's base formation

A series of novel cardo-polymers was prepared using a polymerisation reaction based on Trogers base formation. The precursor dianiline monomers are readily available from the reactions between appropriate anilines and cyclic ketones. One adamantyl-based cardo-polymer displays intrinsic microporosity with an apparent BET surface area of 615 m2 g−1. This polymer demonstrates a combination of good solubility and high molecular mass facilitating the solvent casting of robust films suitable for gas permeability measurements. The intrinsic microporosity of the polymer provides high gas permeabilities and moderate selectivities with particular promise for gas separations involving hydrogen.

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.