Aromatic polyamides containing trityl substituted triphenylamine: Gas transport properties and molecular dynamics simulations

Structure-Property Relationship on the Example of Gas Separation Characteristics of Poly(Arylene Ether Ketone)s and Poly(Diphenylene Phtalide)

Three poly(arylene ether ketone)s (PAEKs) with propylidene (C1, C2) and phtalide (C3) fragments, and one phtalide-containing polyarylene (C4), were synthesized. Their chemical structures were confirmed via 1H NMR, 13C NMR and 19F NMR spectroscopy. The polymers have shown a high glass transition temperature (>155 °C), excellent film-forming properties, and a high free volume for this polymer type. The influence of various functional groups in the structure of PAEKs was evaluated. Expectedly, due to higher free volume the introduction of hexafluoropropylidene group to PAEK resulted in higher increase of gas permeability in comparison with propylidene group. The substitution of the fluorine-containing group on a rigid phtalide moiety (C3) significantly increases glass transition temperature of the polymer while gas permeation slightly decreases. Finally, the removal of two ether groups from PAEK structure (C4) leads to a rigid polymer chain that is characterized by highest free volume, gas permeability and diffusion coefficients among the PAEKs under investigation. Methods of modified atomic (MAC) and bond (BC) contributions were applied to estimate gas permeation and diffusion. Both techniques showed reasonable predicted parameters for three polymers while a significant underestimation of gas transport parameters was observed for C4. Gas solubility coefficients for PAEKs were forecasted by "Short polymer chain surface based pre-diction" (SPCSBP) method. Results for all three prediction methods were compared with the ex-perimental data obtained in this work. Predicted parameters were in good agreement with ex-perimental data for phtalide-containing polymers (C3 and C4) while for propylidene-containing poly(arylene ether ketone)s they were overestimated due to a possible influence of propylidene fragment on indices of oligomeric chains. MAC and BC methods demonstrated better prediction power than SPCSBP method.

Structure-Gas Barrier Property Relationship in a Novel Polyimide Containing Naphthalene and Amide Groups: Evaluation by Experiments and Simulations

In order to meet the increasingly stringent requirements for heat resistance and barrier properties in the packaging and electronic device encapsulation field. A high-barrier polyimide (NAPPI) contains naphthalene ring and amide group was prepared by polymerization of a novel diamine (NAPDA) and pyromellitic dianhydride. The structure and properties of diamine monomers and polymers were characterized. Results show that the NAPPI exhibits superior barrier properties with extremely low water vapor and oxygen transmission rate values of 0.14 g·m⁻²·day⁻¹ and 0.04 cm³·m⁻²·day⁻¹, respectively. In addition, the NAPPI presents outstanding mechanical properties and thermal stability as well. This article attempts to explore the relationship between NAPPI structure and barrier properties by combining experiment and simulation. Studies on positron annihilation lifetime spectroscopy, Wide angle X-ray diffractograms and molecular dynamics simulations prove that the NAPPI has smaller interplanar spacing and higher chain regularity. In addition, the strong chain rigidity and interchain cohesion of NAPPI due to the presence of the rigid naphthalene ring and a large number of hydrogen bond interactions formed by amide groups result in compact chain packing and smaller free volume, which reduces the solubility and diffusibility of small molecules in the matrix. In general, the simulation results are consistent with the experimental results, which are important for understanding the barrier mechanism of NAPPI.

Structure and Gas Barrier Properties of Polyimide Containing a Rigid Planar Fluorene Moiety and an Amide Group: Insights from Molecular Simulations

A novel diamine (FAPDA) bearing rigid planar fluorene and amide groups was successfully synthesized. Using such diamine and pyromellitic dianhydride (PMDA), a high-barrier polyimide (FAPPI) was obtained. FAPPI exhibits an outstanding gas barrier. Its water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) are as low as 0.51 g·m^-2·day^-1 and 0.43 cm³·m^-2·day^-1, respectively. Additionally, FAPPI shows excellent thermal stability with a coefficient of thermal expansion (CTE) of 5.8 ppm·K^-1 and a glass transition temperature (T _g) of 416 °C. Molecular simulations, positron annihilation, and X-ray diffraction were utilized to gain insight on the microstructures for the enhanced barrier properties. Introducing fluorene moieties and amide groups improves the regularity and rigidity of molecular chains and increases interchain interaction of PI, resulting in low free volumes and decreased movement capacity of the chain. The low free volumes of FAPPI restrain the gas diffusivity and solubility. Meanwhile, the decreased chain movement reduces the diffusivity of gases. Consequently, barrier performances of FAPPI are improved. The polyimide possesses widespread application in the microelectronics packaging fields.

Aromatic polyamide nonporous membranes for gas separation application

Polymer membrane-based gas separation is a superior economical and energy-efficient separation technique over other conventional separation methods. Over the years, different classes of polymers are investigated for their membrane-based applications. The need to search for new polymers for membrane-based applications has been a continuous research challenge. Aromatic polyamides (PAs), a type of high-performance materials, are known for their high thermal and mechanical stability and excellent film-forming ability. However, their insolubility and processing difficulty impede their growth in membrane-based applications. In this review, we will focus on the PAs that are investigated for membrane-based gas separations applications. We will also address the polymer design principal and its effects on the polymer solubility and its gas separation properties. Accordingly, some of the aromatic PAs developed in the authors’ laboratory that showed significant improvement in the gas separation efficiency and placed them in the 2008 Robeson upper bound are also included in this review. This review will serve as a guide to the future design of PA membranes for gas separations.

Synthesis and gas transport properties of sulfonated poly(ether ether sulfone) membranes containing pendant sulfonic acid groups

A series of gas separation membranes based on sulfonated poly(ether ether sulfone)s (SPEESs) can be synthesized by the polycondensation and sulfonation reactions. The structural characteristics of copolymers were confirmed by 1H-NMR spectroscopy, Fourier-transform infrared spectroscopy, gel permeation chromatography, and ultraviolet–visible absorption spectroscopy. The permeability and selectivity behavior of these membranes were investigated using three single-gases (CO2, O2, and N2) at different temperatures of 25–55°C and pressures of 1.0–3.0 atm. The effect of sulfonation degree (SD), operating temperature, and pressure on gas permeability was explored and discussed. The results showed that SPEESs containing pendant sulfonic acid groups exhibited different separation performance. In particular, the SPEES-4 membrane with an SD of 67% exhibited the highest permeability (CO2 = 513.8 Barrer and O2 = 78.19 Barrer) at 55°C and 1 atm, whereas CO2/N2 and O2/N2 selectivity was 31.09 and 4.73, respectively.

Interaction of Several Toxic Heterocarbonyl Gases with Polypyrrole as a Potential Gas Sensor

The interactions of the toxic heterocarbonyl gases phosgene, carbonyl fluoride, formaldehyde, carbonyl sulfide, and acetone with polypyrrole as a toxic heterocarbonyl gas sensor, were extensively studied by density functional theory (DFT). The Becke 3-parameter, Lee-Yang-Parr (B3LYP) exchange-correlation functional methods were first tested against several high-level DFT methods employing the Dunning’s double-ζ and triple-ζ basis sets and were found to be sufficient in describing the non-covalent interactions involved in this study. The interaction of pyrrole with the heterocarbonyl gases resulted in changes in the structure and optoelectronic properties of the polymer and it was observed that acetone and formaldehyde had the strongest H-bonding interaction with polypyrrole, while the interaction of phosgene and formaldehyde resulted in the lowest energy gap and may result in its high sensitivity towards these gases. The UV-Vis absorption revealed significant red-shifted first singlet excited states (Eexcited, 1st) of the complexes and follows the same trend as the EGap values. It is shown that the Eexcited, 1st was due to the π(HOMOPy) ⟶ π*(LUMOHC) transitions and the excited state at maximum absorption (Eexcited, max) was due to the π(HOMOPy) ⟶ π*(LUMOPy) transitions. This study demonstrates the potential sensitivity and selectivity of polypyrrole as a toxic heterocarbonyl sensor.

Structure and Properties of High and Low Free Volume Polymers Studied by Molecular Dynamics Simulation

Using molecular dynamics, a comparative study was performed of two pairs of glassy polymers, low permeability polyetherimides (PEIs) and highly permeable Si-containing polytricyclononenes. All calculations were made with 32 independent models for each polymer. In both cases, the accessible free volume (AFV) increases with decreasing probe size. However, for a zero-size probe, the curves for both types of polymers cross the ordinate in the vicinity of 40%. The size distribution of free volume in PEI and highly permeable polymers differ significantly. In the former case, they are represented by relatively narrow peaks, with the maxima in the range of 0.5–1.0 Å for all the probes from H2 to Xe. In the case of highly permeable Si-containing polymers, much broader peaks are observed to extend up to 7–8 Å for all the gaseous probes. The obtained size distributions of free volume and accessible volume explain the differences in the selectivity of the studied polymers. The surface area of AFV is found for PEIs using Delaunay tessellation. Its analysis and the chemical nature of the groups that form the surface of free volume elements are presented and discussed.

Fluorine in the structure of polymers: influence on the gas separation properties

Results of studies on the separation of gases and vapours using fluorine-containing polymers are integrated and analyzed. Methods for the synthesis of these polymers are considered, including direct gas-phase fluorination, plasma polymerization of fluorine-containing precursors and modification of organic polymers, as well as diverse syntheses of monomers containing C−F and C−CF3 bonds and their subsequent polymerization. Structure – property relationships for these polymers are elucidated and their actual and potential applications as membrane materials are discussed.

The bibliography includes 165 references.

Synthesis and gas transport properties of novel poly(ether ether ketone)s containing fluorene group

Two novel gas separation membranes (Phenyl(Ph)-poly(ether ether ketone)s (PEEKs) and PEEKs) based on PEEKs with a high fractional free volume were designed and synthesized. The structure and thermodynamic stability of the membranes were investigated using Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and thermogravimetric analysis. The two membranes, which were determined to be high-molecular weight polymers by gel permeation chromatography, showed good solubility in a weakly polar solvent. The gas transport properties of the Ph-PEEK membranes were investigated for different gases (CO2, O2, CH4, and N2) at 25°C and 1 atm. The Ph-PEEK-3 membrane with the largest free volume had the largest gas permeability coefficient and maintained good selectivity. The effect of operating temperature on the gas permeation of the Ph-PEEK-3 membrane was also investigated, and the maximum permeability of the four single gases was reached at 55°C and 1 atm.

Synthesis and Gas-Permeation Characterization of a Novel High-Surface Area Polyamide Derived from 1,3,6,8-Tetramethyl-2,7-diaminotriptycene: Towards Polyamides of Intrinsic Microporosity (PIM-PAs)

A triptycene-based diamine, 1,3,6,8-tetramethyl-2,7-diamino-triptycene (TMDAT), was used for the synthesis of a novel solution-processable polyamide obtained via polycondensation reaction with 4,4'-(hexafluoroisopropylidene)bis(benzoic acid) (6FBBA). Molecular simulations confirmed that the tetrasubstitution with ortho-methyl groups in the triptycene building block reduced rotations around the C⁻N bond of the amide group leading to enhanced fractional free volume. Based on N₂ sorption at 77 K, 6FBBA-TMDAT revealed microporosity with a Brunauer⁻Emmett⁻Teller (BET) surface area of 396 m² g-1; to date, this is the highest value reported for a linear polyamide. The aged 6FBBA-TMDAT sample showed moderate pure-gas permeabilities (e.g., 198 barrer for H₂, ~109 for CO₂, and ~25 for O₂) and permselectivities (e.g., αH₂/CH₄ of ~50) that position this polyamide close to the 2008 H₂/CH₄ and H₂/N₂ upper bounds. CO₂⁻CH₄ mixed-gas permeability experiments at 35 °C demonstrated poor plasticization resistance; mixed-gas permselectivity negatively deviated from the pure-gas values likely, due to the enhancement of CH₄ diffusion induced by mixing effects.

3-Aminopropyltriethoxysilane-aided cross-linked chitosan membranes for gas separation: grand canonical Monte Carlo and molecular dynamics simulations

Molecular simulations were performed to consider the structural and transport properties of chitosan/3-aminopropyltriethoxysilane (APTEOS) mixed matrix membranes (MMMs). In order to consider the presence of APTEOS content on the performances of membrane, various amounts of APTEOS were added to the polymeric matrix as a cross-linker. Structural characterizations such as radial distribution function (RDF), fractional free volume (FFV) and X-ray diffraction (XRD) were carried out on the simulated cells. Self-diffusivity and solubility of membranes were calculated using mean square displacement (MSD) and adsorption isotherms, respectively. Additionally, permeability and permselectivity of CO₂ and N₂ gases were calculated by grand canonical Monte Carlo and molecular dynamics methods. The system temperature was set to 298 K using a Nose-Hoover thermostat. According to the results, upon increasing APTEOS loading, CO₂ permeability increases until 10 wt.% loading. Then, by adding 20 wt.% of APTEOS, CO₂ permeability decreases, which could be related to higher crystallinity. XRD graphs indicated that the crystallinity decreased when adding 10 wt.% APTEOS, while higher APTEOS content (up to 20 wt.%) led to higher crystallinity percentage, consistent with permeability results. Compared to literature reports, the present simulation indicated higher accuracy for defining the structural and transport properties of APTEOS cross-linked chitosan MMMs. Graphical abstract 3-Aminopropyltriethoxysilane-aided cross-linked chitosan membranes for gasseparation.

Synthesis and gas transport properties of polyamide membranes containing PDMS groups

A series of gas-separation polyamide-poly(dimethylsiloxane) (PA-PDMS) membranes containing PDMS groups were synthesized through the polycondensation reaction. The structural characteristics of polymers were evaluated by ¹H-NMR spectroscopy (NMR), Fourier-transform infrared spectroscopy (FTIR) and UV-vis absorption spectroscopy. The permeability and selectivity behavior was studied at different temperatures (25–55 °C) and pressures (1.0–3.0 atm), using various gases, such as H₂, O₂, CO₂, CH₄, and N₂. The effect of chemical structure, PDMS content, operating pressure and temperature on gas permeability was explored and discussed. Gas-permeation measurements showed that polyamides containing PDMS groups exhibited different separation performance. The PA-PDMS-20 membrane with 20 wt% PDMS exhibited the highest selectivity (CO₂/N₂ = 41.84 and O₂/N₂ = 7.01) at 35 °C and 3.0 atm while CO₂ and O₂ permeability was 29.29 barrer and 4.91 barrer, respectively.

PA-PDMS membranes were synthesized by polycondensation reaction and the gas permeability was found to increase with an increase of PPG content, with the gas permeability of PA-PDMS-20 membrane reaching 29.29 at 35 °C and 3.0 atm.

Polyimides Containing Phosphaphenanthrene Skeleton: Gas-Transport Properties and Molecular Dynamics Simulations

A series of new semifluorinated polyimide (PI) films with phosphaphenanthrene skeleton were prepared by thermal imidization of poly(amic acid)s derived from a diamine monomer: 1,1-bis[2'-trifluoromethyl-4'-(4″-aminophenyl)phenoxy]-1-(6-oxido-6H-dibenz⟨c,e⟩⟨1,2⟩oxaphosphorin-6-yl)ethane on reaction with four structurally different aromatic dianhydrides. The chemical structures of the polymers were established by Fourier transform infrared and 1H NMR spectroscopy techniques. The polymers showed a good combination of thermal and mechanical properties (T d10 up to 416 °C under synthetic air and tensile strength up to 91 MPa), low dielectric constant (2.10-2.55 at 1 MHz), and T g values as high as 261 °C. Gas permeabilities of these films were investigated for four different gases CO2, O2, N2, and CH4. The PI films showed high gas permeability (P CO2 up to 175 and P O2 up to 64 barrer) with high permselectivity (P CO2 /P CH4 up to 51 and P O2 /P N2 up to 7.1), and the values are better than those of many other similar polymers reported earlier. For the O2/N2 gas pair, the PIs (PI A) surpassed the present upper boundary limit drawn by Robeson. A detailed molecular dynamics (MD) simulation study has been conducted to understand better the gas-transport properties. The effect of phosphaphenanthrene skeleton, its spatial arrangement, and size distribution function of the free volume were studied using molecular dynamics (MD) simulation and the results are correlated with the experimental data.

Synthesis and Electrochromism of Highly Organosoluble Polyamides and Polyimides with Bulky Trityl-Substituted Triphenylamine Units

Two series of polyamides and polyimides containing bulky trityl-substituted triphenylamine units were synthesized from condensation reactions of 4,4′-diamino-4′′-trityltriphenylamine with various dicarboxylic acids and tetracarboxylic dianhydrides, respectively. The polymers showed good solubility and film-forming ability. Flexible or robust films could be readily obtained via solution-casting. The use of aliphatic diacid or dianhydride reduces interchain charge transfer complexing and leads to colorless polyamide and polyimide films. These polymers showed glass-transition temperatures in the range of 206–336 °C. Cyclic voltammograms of the polyamide and polyimide films displayed reversible electrochemical oxidation processes in the range of 0–1.0 or 0–1.3 V. Upon oxidation, the color of polymer films changes from colorless to blue-green or blue. As compared to the polyimide counterparts, the polyamides showed lower oxidation potentials and thus a higher electrochromic stability and coloration efficiency. Simple electrochromic devices were also fabricated as a preliminary investigation for electrochromic applications of the prepared polymers.

Aromatic polyamides and copolyamides containing fluorene group

A series of new aromatic polyamides (PAs) and copolyamides (CPAs) containing fluorene group have been synthesized through polycondensation reaction. The chemical structure was confirmed by Fourier transform infrared and proton nuclear magnetic resonance (1H NMR). PAs and CPAs exhibited the higher thermal stability ( Td15 > 378°C in nitrogen), the higher glass transition temperature ( Tg > 345°C), and excellent solubility in polar solvent. Gas transport properties of the PA and CPA membranes were investigated using different single gases (hydrogen (H2), carbon dioxide (CO2), oxygen (O2), methane (CH4), and nitrogen (N2)). We discussed the effect of chemical structure and operating temperature on gas transport properties. The results show that PA-1 containing a hexafluoroisopropylidene moiety exhibited the highest gas permeability ( PH2 = 12.71 Barrer, PCO2 = 12.26 Barrer, and PO2 = 2.62 Barrer) and reasonably good selectivity ( α(H2/N2) = 27.63, α(CO2/N2) = 26.65, and α(O2/N2) = 5.70) at 25°C and 1 atm. For all the membranes, gas permeability gradually increased with the increase in operating temperature, while the selectivity gradually decreased. These gas permeation results were well correlated with fractional free volume, interchain d-spacing ( dsp), and intermolecular interaction.

Functional Aromatic Polyamides

We describe herein the state of the art following the last 8 years of research into aromatic polyamides, wholly aromatic polyamides or aramids. These polymers belong to the family of high performance materials because of their exceptional thermal and mechanical behavior. Commercially, they have been transformed into fibers mainly for production of advanced composites, paper, and cut and fire protective garments. Huge research efforts have been carried out to take advantage of the mentioned characteristics in advanced fields related to transport applications, optically active materials, electroactive materials, smart materials, or materials with even better mechanical and thermal behavior.

Gas separation properties of Troeger’s base-bridged polyamides

A series of new polyamides (PAs) has been prepared from a Troeger base-bridged diamine (TB), 2,8- diamino-4,10-dimethyl-6H,12H-5,11-methanodibenzo[1,5]-diazocine and different commercially available diacid monomers via the conventional polycondensation method. Dense membranes were prepared from the PAs by solution casting and solvent evaporation techniques. The synthesized PAs showed high glass transition temperature (283–290°C), 10% weight loss up to temperature 431°C in air, and tensile strength up to 91 MPa. The PA membranes showed higher permeability than some commercially used glassy polymers (PCO2 up to 109 and PO2 up to 21 Barrer) and permselectivity (PCO2/PCH4 up to 53.7 and PO2/PN2 up to 7.52) in comparison to many other PAs published in the literature.

Soluble, optically transparent polyamides with a phosphaphenanthrene skeleton: synthesis, characterization, gas permeation and molecular dynamics simulations

Soluble, optically transparent polyamides with a phosphaphenanthrene skeleton: synthesis, characterization, gas permeation and molecular dynamics simulations.