New materials for gas separation applications: Mixed matrix membranes made from linear polyimides and porous polymer networks having lactam groups

Producción CientíficaA set of mixed matrix membranes (MMMs) has been prepared by incorporating a triptycene-isatin porous polymer network (PPN) to three aromatic polyimides (one commercial, Matrimid, and two synthesized by us: 6FDA–6FpDA and 6FDA–TMPD) covering a wide range of performances for gas separation. The triptycene-isatin PPN is a highly microporous network having a high CO2 uptake and high chemical and thermal stability. The good compatibility between the components (PPN content of 15 and 30% w/w) was supported by the increase in the glass transition temperature of MMMs relative to the pure polyimide membranes. The addition of the PPN particles improved the permeability of all the gases tested, by increasing diffusivity and, in some cases, gas solubility. The improvements were particularly noticeable in Matrimid-based MMMs, where gas permeability increased by 700%, whereas CO2/N2 and CO2/CH4 ideal selectivities decreased by a mere 4% and 12%, respectively.Ministerio de Economía, Industria y Competitividad (projects MAT2016−76413-C2-R2, MAT2016− 76413-C2-R1, MAT2015−69844-R and CTQ2016−80913- P)Junta de Castilla y León (projects VA248U13 and VA051P17

Microporous Polymer Networks for Carbon Capture Applications

Producción CientíficaA new generation of porous polymer networks has been obtained in quantitative yield by reacting two rigid trifunctional aromatic monomers (1,3,5-triphenylbenzene and triptycene) with two ketones having electron-withdrawing groups (trifluoroacetophenone and isatin) in superacidic media. The resulting amorphous networks are microporous materials, with moderate Brunauer–Emmett–Teller surface areas (from 580 to 790 m2 g–1), and have high thermal stability. In particular, isatin yields networks with a very high narrow microporosity contribution, 82% for triptycene and 64% for 1,3,5-triphenylbenzene. The existence of favorable interactions between lactams and CO2 molecules has been stated. The materials show excellent CO2 uptakes (up to 207 mg g–1 at 0 °C/1 bar) and can be regenerated by vacuum, without heating. Under postcombustion conditions, their CO2/N2 selectivities are comparable to those of other organic porous networks. Because of the easily scalable synthetic method and their favorable characteristics, these materials are very promising as industrial adsorbents.Ministerio de Economía, Industria y Competitividad (grants MAT2013-45071-R / MAT2016-76413-C2-R1 / MAT2016-76413-C2-R2 / MAT2015-69844-R / CTQ2016-80913-P / CTQ2014-52796-P)Junta de Castilla y León (projects VA248U13 / VA051P17

Gas separation membranes obtained by partial pyrolysis of polyimides exhibiting polyethylene oxide moieties

Aromatic copolyimides (PIx) and aromatic-aliphatic copolyimides (PIxEOy) were synthesized by reacting 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) with mixtures obtained from 2,2′-bis(4-aminophenyl)hexafluoropropane (6FpDA), 5-diaminobenzoic acid (DABA) and Jeffamine ED-2003 (PEO). The selective thermal removal of PEO from PIxEOy yielded membranes with high thermal stability and good mechanical properties. The presence of carboxylic groups minimized the shrinkage during the cross-linking process. The membranes containing 10 mol% DABA exhibited good O2/N2 and CO2/CH4 separation performance, and resistance to CO2 plasticization. PIx/PIxEOy blends containing less than 10 wt% PEO were prepared. The CO2/CH4 selectivity/permeability balance of cross-linked membranes largely exceeded that of PIx. The results highlight a possible strategy for using analogous cross-linkable polymers exhibiting ethylene oxide moieties as mere additive to prepare high free volume polyimide's membranes, exhibiting enhanced separation properties and high resistance to plasticization.This work was supported by the Spanish Government (AEI) through projects PID2019-109403RB-C21, PID2019-109403RB-C22 and PID2020-118547 GB-I00, and by the Regional Government of Castilla y León and the EU-FEDER program (CLU2017-09, UIC082, VA088G19 and VA224P20). M.G. acknowledges support of this work from the University of Oklahoma (VPR OfficePeer reviewe

Familial hypercholesterolaemia in children and adolescents from 48 countries: a cross-sectional study

Background: Approximately 450 000 children are born with familial hypercholesterolaemia worldwide every year, yet only 2·1% of adults with familial hypercholesterolaemia were diagnosed before age 18 years via current diagnostic approaches, which are derived from observations in adults. We aimed to characterise children and adolescents with heterozygous familial hypercholesterolaemia (HeFH) and understand current approaches to the identification and management of familial hypercholesterolaemia to inform future public health strategies. Methods: For this cross-sectional study, we assessed children and adolescents younger than 18 years with a clinical or genetic diagnosis of HeFH at the time of entry into the Familial Hypercholesterolaemia Studies Collaboration (FHSC) registry between Oct 1, 2015, and Jan 31, 2021. Data in the registry were collected from 55 regional or national registries in 48 countries. Diagnoses relying on self-reported history of familial hypercholesterolaemia and suspected secondary hypercholesterolaemia were excluded from the registry; people with untreated LDL cholesterol (LDL-C) of at least 13·0 mmol/L were excluded from this study. Data were assessed overall and by WHO region, World Bank country income status, age, diagnostic criteria, and index-case status. The main outcome of this study was to assess current identification and management of children and adolescents with familial hypercholesterolaemia. Findings: Of 63 093 individuals in the FHSC registry, 11 848 (18·8%) were children or adolescents younger than 18 years with HeFH and were included in this study; 5756 (50·2%) of 11 476 included individuals were female and 5720 (49·8%) were male. Sex data were missing for 372 (3·1%) of 11 848 individuals. Median age at registry entry was 9·6 years (IQR 5·8-13·2). 10 099 (89·9%) of 11 235 included individuals had a final genetically confirmed diagnosis of familial hypercholesterolaemia and 1136 (10·1%) had a clinical diagnosis. Genetically confirmed diagnosis data or clinical diagnosis data were missing for 613 (5·2%) of 11 848 individuals. Genetic diagnosis was more common in children and adolescents from high-income countries (9427 [92·4%] of 10 202) than in children and adolescents from non-high-income countries (199 [48·0%] of 415). 3414 (31·6%) of 10 804 children or adolescents were index cases. Familial-hypercholesterolaemia-related physical signs, cardiovascular risk factors, and cardiovascular disease were uncommon, but were more common in non-high-income countries. 7557 (72·4%) of 10 428 included children or adolescents were not taking lipid-lowering medication (LLM) and had a median LDL-C of 5·00 mmol/L (IQR 4·05-6·08). Compared with genetic diagnosis, the use of unadapted clinical criteria intended for use in adults and reliant on more extreme phenotypes could result in 50-75% of children and adolescents with familial hypercholesterolaemia not being identified. Interpretation: Clinical characteristics observed in adults with familial hypercholesterolaemia are uncommon in children and adolescents with familial hypercholesterolaemia, hence detection in this age group relies on measurement of LDL-C and genetic confirmation. Where genetic testing is unavailable, increased availability and use of LDL-C measurements in the first few years of life could help reduce the current gap between prevalence and detection, enabling increased use of combination LLM to reach recommended LDL-C targets early in life

Effect of the Acid Medium on the Synthesis of Polybenzimidazoles Using Eaton’s Reagent

The influence of trifluoromethanesulfonic (TFSA) superacid on conditions of the synthesis of polybenzimidazoles, such as OPBI and CF3PBI, was studied. It was shown that the polycondensations proceeded smoother and at lower temperatures in the presence of the TFSA in Eaton’s Reagent and that polymers of high molecular weights, and readily soluble in organic solvents, were obtained. The effect was more pronounced for CF3PBI, where the low reactivity monomer, 4,4′ (hexafluoroisoproylidene)bis (benzoic acid), was used. CF3PBI was obtained at a moderate temperature of 140 °C with no gel fraction and exhibited an inherent viscosity twice higher than the one obtained by the traditional method. In fact, the addition of TFSA allows the obtention of soluble N-phenyl substituted CF3PBI by direct synthesis, which had not been obtained otherwise. Thus, the use of TFSA is a good media for the synthesis of N-substituted PBIs under relatively mild conditions

Gas Permeation Properties of Soluble Aromatic Polyimides Based on 4-Fluoro-4,4'-Diaminotriphenylmethane

A series of new organic polyimides were synthesized from 4-fluoro-4'4"-diaminotriphenylmethane and four different aromatic dianhydrides through a one-step, high-temperature, direct polycondensation in m-cresol at 180–200 °C, resulting in the formation of high-molecular-weight polyimides (inherent viscosities ~ 1.0–1.3 dL/g). All the resulting polyimides exhibited good thermal stability with initial decomposition temperatures above 434 °C, glass-transition temperatures between 285 and 316 °C, and good solubility in polar aprotic solvents. Wide-angle X-ray scattering data indicated that the polyimides were amorphous. Dense membranes were prepared by solution casting and solvent evaporation to evaluate their gas transport properties (permeability, diffusivity, and solubility coefficients) toward pure hydrogen, helium, oxygen, nitrogen, methane, and carbon dioxide gases. In general, the gas permeability was increased as both the fractional free volume and d-spacing were also increased. A good combination of permeability and selectivity was promoted efficiently by the bulky hexafluoroisopropylidene and 4-fluoro-phenyl groups introduced into the polyimides. The results indicate that the gas transport properties of these films depend on both the structure of the anhydride moiety, which controls the intrinsic intramolecular rigidity, and the 4-fluoro-phenyl pendant group, which disrupts the intermolecular packing

Thermally Rearranged Polybenzoxazoles Containing Bulky Adamantyl Groups from Ortho-Substituted Precursor Copolyimides

A new nucleophilic monomer (2,2-bis(3-amino-4-hydroxyphenyl)adamantane, ADHAB) having bulky adamantane groups has been synthesized following an efficient synthetic methodology. The main target of this work was to employ a high thermal stable bulky cycloaliphatic moiety as adamantane to obtain aromatic ortho-hydroxypolyimides (poly(o-hydroxyimide)s) able to thermally rearrange to give polybenzoxazole (TR-PBO) materials that could be tested as gas separation membranes. Thus, an array of ortho-acetylcopolyimides, o-acetyl PIs) were prepared by reaction of ADHAB and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (APAF) with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) via chemical imidization. Copolyimides and homopolyimides showed inherent viscosities ranging from 0.49 to 0.70 dL/g and provided good-quality dense membranes. Glass transition temperatures of these o-acetyl copolyimides were higher as the amount of ADHAB increased. The thermal stability of the adamantane moiety during the TR process was evaluated by directly synthesizing PBOs, which were made from the reaction, and ulterior thermal cyclization, of 2,2-bis(4-chlorocarbonylphenyl)-hexafluoropropane with ADHAB/APAF. TR-PBO membranes made through a thermal treatment at 450 °C for 30 min showed excellent gas separation properties for the CO/CH gas pair with values close to the 2008 Robeson limit.The authors acknowledge financial support provided by Spain’s MINECO (CTQ2013-48406-P, MAT2016-76413-C2-R1, and MAT2016-76413-C2-R2). This research was also supported by the Korea Carbon Capture & Sequestration R&D Center (KCRC) administered through the National Research Foundation of Korea (NRF) funded by the Ministry of S c i e n c e , IC T , a n d Fu t u r e Pl anni n g (NRF - 2014M1A8A1049305). We are also indebted to the Spanish Junta de Castilla y León for funding help (Projects VA248U13 and VA256U13). C. Aguilar-Lugo gratefully acknowledges a CONACYT postdoctoral fellowship (264013).Peer Reviewe

Synthesis and properties of highly processable asymmetric polyimides with bulky phenoxy groups

A series of new aromatic polyimides (PIs) and co-PIs containing bulky tert-butyl phenoxy group was synthesized by one-step high-temperature polycondensation of 1,3-diamino-4-(4′-tert-butylphenoxy)benzene (tBuPDAB) with different commercially available aromatic dianhydrides. The polymers were obtained in quantitative yields with inherent viscosities of 0.40–0.70 dL g. They exhibited high thermal stability with 10% weight loss above 480°C and were cast in films with good mechanical properties capable to be tested as gas separation membranes. These PIs were compared with analogs bearing phenoxy group (PDAB). The incorporation of tBu improved the solubility of the PIs, their free volume fraction, d-spacing, and gas permeability coefficients in comparison with their analogs obtained from PDAB. The permeability enhancement was from 2.5 to 8 times depended on the gas tested. The PI, based on tBuPDAB and 4,4’-(hexafluoroisopropylidene)diphtalic anhydride and, thus, containing two different bulky pendant groups, showed the highest gas permeability coefficient for CO (58.3 Barrer) and moderate ideal selectivity to the gas pair CO/CH (α = 18.0)

Aromatic polyimides and copolyimides containing bulky t-butyltriphenylmethane units

Triphenylmethane-based polyimides and copolyimides containing bulky t-butyl group (tBu) were obtained by one-step high temperature polycondensation of 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride with diamines of triphenylmethane (TPM) family. The polymers were obtained in quantitative yields with inherent viscosities of 0.45–0.80 dL/g. They exhibited high thermal stability with 5% weight loss above 500 °C and were cast in films with good mechanical properties capable of testing as gas separation membranes. All polyimides were readily soluble in polar aprotic solvents, and the solubility enhanced with the increase in tBu-group content. The amorphous, free-standing membranes were prepared from these polymers, and their permeabilities and selectivities to several gases were measured and discussed with respect to the structural differences in the polymers. It was shown that the presence of bulky tBu-units made the chain packing less efficient; free volume and d-spacing in the polyimides grew accordingly. As a consequence, the membranes with higher content of tBu-groups demonstrated improved permeabilities, showing 1.5–3.0 times higher permeability coefficients depending on the gas tested. The membranes’ separation performance was improved for CO/CH gas pair in comparison with that of structurally similar polyimides, while it did not change for O/N pair. Additionally, the mechanism of formation of triphenylmethane diamines in the reaction between aniline and benzaldehydes was investigated in order to optimize the monomer synthesis and to minimize possible side reactions. It was established that the secondary diamines, so-called aminals, were inevitable side products, particularly important in the condensation between aniline and tBu-benzaldehyde.This work was supported by grants from DGAPA # IN107117 and by Spain’s MINECO (Projects MAT2016-76413-C2-R2, and MAT2016-76413-C2-R1). The authors thank G. Cedillo Valverde, M.A. Canseco Martinez, E. Hernandez Mecinas, E. R-Morales and A. Tejeda Cruz (all from IIM-UNAM) for different kinds of analyses and also would like to acknowledge Sara Rodriguez for the gas separation measurements. R.A.C.B. is grateful to CONACyT for the financial support

Isomeric Aromatic Polyimides Containing Biphenyl Moieties for Gas Separation Applications

An optimized synthesis of the monomer 2,2′3,3′-biphenyltetracarboxylic dianhydride, iBPDA, was performed to obtain high molecular weight polymers. This monomer has a contorted structure that produces a non-linear shape, hindering the packing of the polymer chain. Aromatic polyimides of high molecular weight were obtained by reaction with the commercial diamine 2,2-bis(4-aminophenyl) hexafluoropropane, 6FpDA, which is a very common monomer in gas separation applications. This diamine has hexafluoroisopropylidine groups which introduce rigidity in the chains, hindering efficient packing. The thermal treatment of the polymers processed as dense membranes had two targets: on the one hand, to achieve the complete elimination of the solvent used, which could remain occluded in the polymeric matrix, and on the other hand to ensure the complete cycloimidization of the polymer. A thermal treatment exceeding the glass transition temperature was performed to ensure the maximum degree of imidization at 350 °C. The good mechanical properties of these materials allow for their use in high-pressure gas purification applications. Moreover, models of the polymers exhibited an Arrhenius-like behavior characteristic of secondary relaxations, normally associated with local motions of the molecular chain. The gas productivity of these membranes was high.This research was funded by the Spanish Government (AEI) through projects PID2019-109403RB-C21 and PID2019-109403RB-C22, and by Spain’s Regional Government of Castilla y León and the EU-FEDER program (CLU2017-09, UIC082 and VA088G19)Peer reviewe