Troger's Base Research Articles

Thermally Rearranged Polymer Membranes Containing Tröger's Base Units Have Exceptional Performance for Air Separations

AbstractThe influence of segmental chain motion on the gas separation performance of thermally rearranged (TR) polymer membranes is established for TR polybenzoxazoles featuring Tröger's base (TB) monomer subunits as exceptionally rigid sites of contortion along the polymer backbone. These polymers are accessed from solution‐processable ortho‐acetate functionalized polyimides, which are readily synthesized as high‐molecular‐weight polymers for membrane casting. We find that thermal rearrangement leads to a small increase in d‐spacing between polymer chains and a dramatic pore‐network reconfiguration that increases both membrane permeability and O2/N2 selectivity, putting its performance above the 2015 upper bound.

A facile synthesis of contorted spirobisindane-diamine and its microporous polyimides for gas separation.

Microporous polyimides (PIM-PIs, KAUST-PIs) and polymers containing Tröger's base (TB) derivatives with improved permeability and selectivity have great importance for separation of environmental gas pairs. Despite the tremendous progress in this field, facile synthesis of microporous polymers at the industrial scale via designing new monomers is still lacking. In this study, a new potential approach for large scale synthesis of spirobisindane diamine (DAS) (3) has been reported from commercially available 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane (TTSBI) and 3,4-difluoronitrobenzene. A series of DAS diamine based microporous polyimides were also synthesized. The resulting polymer membranes showed high mechanical and thermal properties with tunable gas separation performance.

Evaluation of free volume and anisotropic chain orientation of Tröger's base (TB)-based microporous polyimide/copolyimide membranes

Polarization-dependent refractive indices were utilized to probe the free volume and anisotropic chain orientation of several types of microporous polyimides (PIs)/copolyimides (co-PIs) based on Tröger's base (TB). The properties related to the free volume and chain orientation, such as dielectric constants and linear thermal expansion behaviors, as well as the out-of-plane thermal diffusivity (D⊥), were quantitatively investigated. The free volume fractions (Vf) of 0.183–0.228 were estimated for the membranes based on the Lorentz-Lorenz equation and molecular polarizability calculations. The TB-based PIs/co-PIs exhibited relatively low average refractive indices (1.5208–1.6061), low-to-moderate birefringence (0.0181–0.0505) at 1310 nm, and ultra-low D⊥ values ranging from 6.2 to 9.6 × 10−8 m2/s, depending on the chemical structures and the preparation conditions. Their excellent overall performance suggests their potential applications, for example, in protective sunshades, heat insulation tape, and thermal barrier coatings.

Polymers of Intrinsic Microporosity derived from a carbocyclic analogue of Tröger's base

Tröger's base (TB) is often used as a building block for the synthesis of Polymers of Intrinsic Microporosity (PIMs) due to its rigid bicyclic V-shaped structure. In this study the TB component in the structure of a PIM is replaced by 2,3:6,7-dibenzobicyclo[3.3.1]nonane, a purely carbocyclic analogue of TB. This modification results in only a slightly reduced amount of microporosity as determined using nitrogen adsorption. Further comparisons with previously reported PIMs indicate that this building unit (and therefore TB) is significantly less effective for the generation of intrinsic microporosity than spirobisindane, a commonly used structural unit for PIM synthesis. It appears that the V-shape of the 2,3:6,7-dibenzobicyclo[3.3.1]nonane and TB units allows closer contact between polymer chains thereby enhancing packing efficiency.

A structural study of Troger's base scaffold-based dyes for DSSC applications

Three Troger's base scaffold-based metal-free sensitizers TD1, TD2 and TD3 with triphenylamine donor and rhodanine-3-acetic acid as an acceptor/anchoring group were designed and synthesized for dye-sensitized solar cells. The sensitizer series was designed to investigate the influence of the poly[n]enic (from n = 0 to 2) backbones and their anchoring effect in DSSCs. Optical, electrochemical and photovoltaic properties were compared with analogues dyes D1-D3 possessing one anchoring group. It has been proven that the extended polymethine chains ensure flexibility of these units and inspire the interaction between two chromophores promoting aggregate formation in these Troger's base-based dyes.

Molecular design of Tröger’s base-based polymers with intrinsic microporosity for gas separation

High performance polymers with intrinsic microporosity have been prepared via introducing sites of contortion and chain stiffness with the incorporation of Tröger's base (TB). An experimental investigation coupling with computational simulation was executed to study the effects of polymers’ chemical structures on their gas separation performance. A general acid-catalyzed and low-temperature synthetic route was adopted to achieve the polymerization between 1, 5-diaminonaphathelen (1,5-DAN) and 4,4′-(Hexafluoroisopropylidene) dianiline (4,4′-HFD) via condensation and cyclization. It is found that the resultant 1, 5-diaminonaphathelen Tröger's base-based polymer (1,5-DTBP), 4,4′-(Hexafluoroisopropylidene) dianiline Tröger's base-based polymer (4,4′-HTBP) and their copolymers are readily soluble in the N-methyl-2-pyrrolidone (NMP) solvent, cast as free standing films and exhibit good gas separation performance. The TB-based polymer containing 10% 4,4′-HFD has both the highest permeability and acceptable selectivity even exceeding the Robeson upper bound for H2/CH4. Molecularly designed ineffective chain packing via the enhancement of backbone rigidity and introduction of bulky side groups is proved to be the main mechanism that achieves the high separation performance. Since the newly synthesized TB-based polymers display desirable H2/CH4 and H2/N2 gas separation performance approaching the Robeson upper bounds, this work proves the feasibility of designing advanced polymeric materials with Tröger's base as the sole constituent.

Enhancing the Gas Permeability of Tröger’s Base Derived Polyimides of Intrinsic Microporosity

A series of four novel Troger’s base (TB) derived polyimides of intrinsic microporosity (PIM–TB–PI) is reported. The TB diamine monomer (4MTBDA) possesses four methyl groups in order to restrict rotation about the C–N imide bonds in the resulting polymers. The polymers possess apparent BET (Brunauer, Emmett, and Teller) surface areas between 584 and 739 m2 g–1, complete solubility in chloroform, excellent molecular mass, high inherent viscosity and good film-forming properties. Gas permeability measurements demonstrate enhanced performance over previously reported polyimide-based Troger’s base (TB) polymers confirming the benefit of the additional methyl groups within the TB diamine monomer. Notably, a polyimide derived from 4MTBDA and pyromellitic anhydride (PMDA) demonstrates gas permeability data above the 2008 upper bounds for important gas pairs such as O2/N2, H2/N2, and H2/CH4.

Soluble, microporous, Tröger's Base copolyimides with tunable membrane performance for gas separation

A facile two-step synthesis beginning with commercial monomers to prepare copolyimides by Tröger's Base (TB) formation provides membranes for the first time with tunable gas transport relative to hydrogen separations, CO2 plasticization resistance, and good mechanical and thermal properties.

Troger's base functionalized covalent triazine frameworks for CO2 capture

Amorphous, highly thermal stable, Troger's base segments containing covalent triazine frameworks with high CO2 adsorptions (up to 16.84 wt% at 273 K and 1.10 bar).

Rhenium(I)-based Double-heterostranded Helicates

Rhenium(I)-based supramolecular coordination complexes were obtained using Re2(CO)10, (2-hydroxyphenyl)benzimidazole-derived bis-chelating N∩O donors and a benzimidazolyl-derived ditopic monodentate N-donor possessing Troger's base spacer in a one-pot approach.

Microporous Polyimides with Rationally Designed Chain Structure Achieving High Performance for Gas Separation

Polyimides of intrinsic microporosity are important polymers for gas separation. Achieving polyimides with high permeability and high selectivity relies on rationally designing their chain structure. In this work, new ladder-like diamines, Troger’s Base (TB) derived diamines, are designed, and two microporous polyimides are constructed by polymerizing TB-derived diamines and spirobisindane based dianhydride, aiming at enhancing the stiffness of the whole backbone and thus achieving improved performance by taking advantage of the stiffness of both diamines and dianhydride. The two polyimides present excellent separation performance, surpassing the 2008 Robeson upper bound for gas pairs of H2/N2 and O2/N2 and approach the 2008 Robeson upper bound for gas pairs H2/CH4 and CO2/CH4. Our results show that the designed polyimides have great potential for application especially for oxygen (O2/N2) and hydrogen (such as H2/N2 and H2/CH4) related separation.

Supramolecular approach to enantioselective DNA recognition using enantiomerically resolved cationic 4-amino-1,8-naphthalimide-based Tröger's bases.

The synthesis and photophysical studies of two cationic Tröger's base (TB)-derived bis-naphthalimides 1 and 2 and the TB derivative 6, characterized by X-ray crystallography, are presented. The enantiomers of 1 and 2 are separated by cation-exchange chromatography on Sephadex C25 using sodium (-)-dibenzoyl-l-tartarate as the chiral mobile phase. The binding of enantiomers with salmon testes (st)-DNA and synthetic polynucleotides are studied by a variety of spectroscopic methods including UV/vis absorbance, circular dichroism, linear dichroism, and ethidium bromide displacement assays, which demonstrated binding of these compounds to the DNA grooves with very high affinity (K ∼ 10(6) M(-1)) and preferential binding of (-)-enantiomer. In all cases, binding to DNA resulted in a significant stabilization of the double-helical structure of DNA against thermal denaturation. Compound (±)-2 and its enantiomers possessed significantly higher binding affinity for double-stranded DNA compared to 1, possibly due to the presence of the methyl group, which allows favorable hydrophobic and van der Waals interactions with DNA. The TB derivatives exhibited marked preference for AT rich sequences, where the binding affinities follow the order (-)-enantiomer > (±) > (+)-enantiomer. The compounds exhibited significant photocleavage of plasmid DNA upon visible light irradiation and are rapidly internalized into malignant cell lines.

Heterogeneous organocatalysts composed of microporous polymer networks assembled by Tröger's base formation

Microporous polymer networks are assembled from triamino-triptycene monomers using a polymerisation reaction based on the formation of Troger's base (TB). The highly rigid triptycene units ensure that the polymer networks demonstrate significant intrinsic microporosity as demonstrated by apparent surface areas of up to 1000 m2 g−1. These networks act as heterogeneous basic catalysts which enhance greatly the rate of a model Knovenagel reaction between malonontrile and benzaldehyde. Indeed, the microporous networks, which possess a high concentration of basic sites, enhance the rate of the Knovenagel reaction even more efficiently than using Troger's base as a homogeneous catalyst.

The synthesis of microporous polymers using Tröger's base formation

A step-growth polymerisation based on the formation of Troger's 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 Troger's 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.

Synthesis of cardo-polymers using Tröger's base formation

A series of novel cardo-polymers was prepared using a polymerisation reaction based on Troger's 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.

Tröger's Base-Based Microporous Polyimide Membranes for High-Performance Gas Separation.

It is a great challenge for polyimide to increase its permeability and at the same time to maintain its high selectivity. In this work, Tröger's Base (TB)-based polyimides through polymerizing Tröger's Base diamines with two kinds of anhydrides were successfully synthesized to enhance the permeability of polyimides for gas separation. The TB-polyimide membranes exhibited greatly improved gas separation performance for H2/CH4, H2/N2, He/CH4, and CO2/CH4 gas pairs, among which the separation performance of 6-FDA-based TB-polyimides approaches or slightly exceeds the 2008 Robeson upper bound. Our results revealed that the TB unit with rigid and in-built amine structure plays an important role for increasing the permeability of polyimides and simultaneously maintaining high selectivity. In addition, the TB-based polyimide membranes exhibited extremely high solubility selectivity for the CO2/N2 gas pair up to 62.7 due to a strong affinity between CO2 and nitrogen atoms of tertiary amine in TB.

Intrinsically Microporous Soluble Polyimides Incorporating Tröger’s Base for Membrane Gas Separation

Polyimides with intrinsic microporosity were readily prepared by introducing Troger’s base (TB) into the polymer backbone via polymerization between imide-containing diamines and dimethoxymethane (DMM). Two imide-containing diamines were prepared by reaction of 2,5-dimethyl-1,4-phenylenediamine (DPD) with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA). The resulting polyimides were readily soluble in common organic solvents, had good mechanical properties, with tensile strength in the range of 59–64 MPa and elongation at break of 5–17%, good thermal stability and extremely high glass transition temperatures (Tgs), up to 425 °C. The polyimides with incorporated TB units had high fractional free volume (FFV ≥ 0.215) resulting from poor chain-packing and exhibited significant microporosity and good gas transport properties. The novel polymer architecture in this study extends the development of polyimides with intrinsic microporosity fo...

Tröger's base quasiracemates and crystal packing tendencies

A family of 7 Tröger's base (TB) compounds that vary in configuration (quasiracemates, racemates, and enantiomers) and chemical substitutions (Me, Cl, and Br) has been investigated.

Mechanistic insight into highly efficient gas permeation and separation in a shape-persistent ladder polymer membrane

A fully atomistic simulation study is reported to provide mechanistic insight into the superior performance experimentally observed for a polymer membrane (Carta et al., Science, 2013, 339, 303-307). The membrane namely PIM-EA-TB is produced by a shape-persistent ladder polymer of intrinsic microporosity (PIM) with rigid bridged bicyclic ethanoanthracene (EA) and Tröger's base (TB). The simulation reveals that PIM-EA-TB possesses a larger surface area, a higher fraction free volume and a narrower distribution of torsional angles compared to PIM-SBI-TB, which consists of less rigid spirobisindane (SBI). The predicted surface areas of PIM-EA-TB and PIM-SBI-TB are 1168 and 746 m(2) g(-1), close to experimental values of 1120 and 745 m(2) g(-1), respectively. For five gases (CO2, CH4, O2, N2 and H2), the solubility and diffusion coefficients from simulation match well with experimental data, except for H2. The solubility coefficients decrease in the order of CO2 > CH4 > O2 > N2 > H2, while the diffusion coefficients increase following CH4 < CO2 < N2 < O2 < H2. In terms of the separation for CO2/N2, CO2/CH4 and O2/N2 gas pairs, PIM-EA-TB exhibits higher permselectivities than PIM-SBI-TA, in good agreement with experiment. From a microscopic perspective, this simulation study elucidates that the presence of bridged bicyclic units in PIM-EA-TB enhances the rigidity of polymer chains as well as the capability of gas permeation and separation, and the bottom-up insight could facilitate the rational design of new high-performance membranes.

Polymers of Intrinsic Microporosity Containing Tröger Base for CO2 Capture

Properties of four polymers of intrinsic microporosity containing Troger’s base units were assessed for CO2 capture experimentally and computationally. Structural properties included average pore size, pore size distribution, surface area, and accessible pore volume, whereas thermodynamic properties focused on density, CO2 sorption isotherms, and enthalpies of adsorption. It was found that the shape of the contortion site plays a more important role than the polymer density when assessing the capacity of the material, and that the presence of a Troger base unit only slightly affects the amount adsorbed at low pressures, but it does not have any significant influence on the enthalpy of adsorption fingerprint. A comparison of the materials studied with those reported in the literature allowed us to propose a set of guidelines for the design of polymers for CO2 capture applications.