Searching strategies to create highly microporous materials with excellent thermal stability, a family of porous organic polymers (POPs) was synthesized via aromatic electrophilic substitution reactions in superacid media. The networks were prepared by reacting multifunctional aromatic monomers —including 9,9'-spirobifluorene (SBF), triptycene (TR), 1,3,5-triphenylbenzene (TPB), and its derivatives 1,3,5-tri-(2-methylphenyl)benzene (TMB) and 1,3,5-tri-(4-biphenyl)benzene (TBB)— with activated ketones as cross-linkers: 2,2,2-trifluoroacetophenone (TF), 1H-indole-2,3-dione (I), and 1-methylindoline-2,3-dione (MI). Additionally, bifunctional aromatic monomers such as biphenyl (BP) and the rigid, contorted 9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene (DMHEA) were incorporated as co-monomers to modulate the cross-linking density and length.The resulting amorphous POPs exhibited moderate to high surface areas (577-1033 m2 g- 1) and excellent thermal stability (> 450 ºC). Materials derived from TR and TPB using I and MI as cross-linkers exhibited the highest CO2 uptake (5.42–2.94 mmol g-1 at 0 ºC and 1 bar), while those incorporating BP and DMHEA demonstrated lower capacities (3.61-2.10 mmol g-1). TR-based POPs exhibited outstanding thermal stability, ease of regeneration, and optimal selectivity for CO2/N2 (15/85) and CO2/CH4 (50/50) mixtures, maintaining high performance even at elevated pressures for the latter. The results position these POPs as promising candidates for molecular sieving in PSA-based gas separation processes.

Over the last few decades, there has been a dramatic increase in CO2 emissions into the atmosphere, prompting intensified efforts toward CO2 capture. Membranes play a key role in carbon capture technologies due to their energy-effective separation, offering a promising approach to mitigate greenhouse gas emissions, even though the research continues for new materials with improved properties. Among the approaches to improve gas separation, the introduction of nitrogen (N) atoms in the polymer backbone has been demonstrated to be an efficient methodology for tailoring CO2 sorption affinity. Here, we propose a novel class of polyimides made from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6F) with ortho-methyl diamines derived from N-rich 4,5diazafluorene (DF) or a mixture of those with 2,2 '-bis(4-aminophenyl)hexafluoropropane (6Fp) or 2,4,6-trimethyl-m-phenylenediamine (TMPD) in a 1:1 or 1:3 M ratio. The resulting polymers showed good solubility, excellent thermal stability, high glass transition temperatures, and mechanical properties robust enough. The homopolymer membrane derived from the fluorine-free DF moiety with four ortho methyl groups exhibited a 3fold increase in CO2 permeability compared to the reference 6F6Fp membrane with slightly increased CO2/N2 selectivity. More importantly, it showed enhancement in CO2/N2 mixed-gas selectivity by 40 % in a CO2/N2 mixture. The four-month-long physical aging response of the selected DF-containing polyimide was also investigated. This work provides valuable insights on the design of monomers for gas separation materials.

A series of polyimides (PIs) was synthesized from 6FDA and two o-OH substituted diamines having bulky pendant phenyl, Ph, and trifluoromethyl, CF3, groups as precursors for thermally rearranged polybenzoxazole, TR-PBO, membranes. One diamine had two pendant Ph substituents; in the other, the substituents were Ph and CF3. Applying azeotropic and chemical cyclizations allowed the obtention of four o-hydroxy (o-OH) or/and o-acetoxy (o-OAc) substituted PIs depending on the imidization method. The PIs were labeled as 3Ph-OH, 4Ph-OH, or 3Ph-OAc and 4PH-OAc, respectively. Thermal rearrangements of all four precursors were investigated in the interval from 350 to 450 degrees C. The conversions to TR-PBO increased with temperature, and almost quantitative conversions were obtained at temperatures close to 450 degrees C, although o-OH substituted PIs reached conversions slightly higher than those of o-OAc PIs at a given temperature. The TR-polymers' fractional free volume (FFV) also increased with conversion but was higher for the o-OAc substituted precursors. Despite the high TR-PBO conversions, self-supported uniform TR membranes with reasonable mechanical properties were obtained, except for 4Ph-OH. Gas separation behavior of the membranes significantly improved after the thermal treatment, and the final CO2/CH4 permselectivities lay between the 1991 and 2008 Robeson upper bounds. Particularly, TR-membranes derived from o-OAc precursors and with pendant CF3 group demonstrated better gas transport properties with values of P-(CO2) = 1121 barrer and alpha(CO2/CH4) = 29 for 3Ph-OAc derived membrane, which positioned it beyond the 2008 upper limit.

Gas separation properties are reported for self-standing polymer of intrinsic microporosity (PIM) films after addition of palladium (II) acetate or iron (II) acetate by solid state or liquid state mixing. Membranes, with thicknesses in the range 35-55 mu m, were prepared from three high molar mass PIMs, two different branched versions of the much-reported PIM-1 (PIM-1a and PIM-1b) and of PIM-Py. Addition of either Fe(OAc)2 or Pd (OAc)2 to all three PIMs led to a reduction in permeability and increase in selectivity, but the permeability reduction was much greater for Pd(OAc)2, which is able to interact with branch points in the PIM and crosslink the polymer. CO2/CH4 selectivity of membranes containing Pd(OAc)2 was poor upon aging, especially after solid state addition to the PIM-1 polymers, for which CO2 permeabilities dropped to below 200 Barrer after 85 days. Hydrogen permeability and H2/N2 selectivity of membranes containing Pd(OAc)2 did more closely follow conventional permeability/selectivity trade off upon aging. This illustrates the profound differences that can arise in gas permeation properties and aging behaviour from variations in chemical structure and macromolecular characteristics, and from the addition of metal acetates that interact with the polymer in different ways.

Two microporous polymer networks having a confined AuI carbene catalyst were obtained and tested for the skeletal rearrangement of enynes. These catalysts were obtained from precursor porous organic polymers (POPs), a type of microporous polymer network, synthesized by the reaction of isatin or a mixture of isatin/trifluoroacetophenone (1:1) with triptycene (POP1 and POP2, respectively) through an electrophilic aromatic substitution, EAS, reaction promoted by trifluoromethanesulfonic acid. These precursors could be easily functionalized through the lactam moiety to form AuI carbene catalysts (POP1-AuCarbene and POP2-AuCarbene). The confined carbenes proved to be very active for the skeletal rearrangement of dimethyl 2-(3-methyl-2-butenyl)-2-propinylmalonate enyne. A large increase in the stability of the AuI catalysts was observed compared to those of most of the homogeneous catalysts described so far in the bibliography. This long-term stability was associated with the separation of AuI atoms, induced by their confinement in the microporous networks. In particular, POP2-AuCarbene exhibited outstanding long-term stability, maintaining catalytic activity even after several months.

Three aromatic polyimides (PIs) based on diamines containing a biphenyl unit and CF3-groups in the m-position to amines and 6FDA of high-molecular weights were synthesized. The polymers differed by number of methyl-substituents in the biphenyl moiety, as 6FDA-BFAPB, PI without methyl substituents, 6FDA-4MeBFAPB, PI with four methyl groups, and 6FDA-4MeBFAPB, PI with six methyl groups. The comparative analysis of the polymer properties was performed with focus on their gas transport properties. All PIs demonstrated high thermostability, with decomposition temperature above 450 C-degrees in an inert atmosphere and char yield of 45-50% but were readily soluble at room temperature even in common organic solvents. The T- g's of PIs bearing methyl groups were notably higher than that of 6FDA-BFAPB, indicating their more rigid backbone chains. Detailed investigation of the PIs' gas transport properties was also made for pure gases and real gas mixture in the wide interval of pressures. It was shown that introduction of the methyl substituents in the main polymer chain resulted in an important improvement of the gas transport properties; both methylated PIs were located much closer to the Robeson limit.

Sustainable hydrogen production is focused on anion exchange membrane (AEM) water electrolyzers (AEMWEs), which still require more development to achieve high performance and durability. Here, we propose a novel class of porous organic polymers (POPs) as durable solid-ionomers for AEMWEs, which was prepared by reacting the 4-methylpiperidone with trifunctional or a mixture of trifunctional:difunctional aromatic monomers (in a 2 : 3 mol ratio). The resulting POP ionomers exhibited exceptional electrochemical properties and remarkable alkaline stability. Particularly noteworthy are the corresponding AEMWEs, which showed an outstanding current density of 13.4 A cm-2 at 2.0 V under 80 °C in 1 M KOH solution, which is the highest performance reported in the particulate-ionomers AEMWE state of the art. Moreover, they demonstrated durability at a current density of 0.5 A cm-2 for over 500 h with a voltage decay rate of 120 μV h-1. This work offers valuable perspectives on the designing of robust and high-performance solid-state ionomers through low-cost electrophilic aromatic substitution reactions for high-performance energy conversion devices.

Boosting the transport and selectivity properties of membranes based on polymers of intrinsic microporosity (PIMs) toward one specific working analyte of interest is challenging. In this work, a novel family of PIM membranes, prepared by casting and exhibiting optima mechanical properties and high thermal stability, was synthesized from 4,4 '-(2,2,2-trifluoro-1-phenylethane-1,1-diyl) bis(benzene-1,2-diol) and two tetrafluoro-nitrile derivatives. Gas permeability measurements evidenced a CO2/CH4 selectivity up to 170% relative to the reference polymer, PIM-1, in agreement with their calculated fractional free volume and the analysis of the textural properties by N-2 and CO2 gas adsorption. Besides, the chemical modification by acid hydrolysis of the PIM membranes favored the permeability for lithium ions (LiCl 2M, 6 x 10(-9) cm(2)s(-1)) compared to other alkali metal analogs such as sodium (NaCl 2M, 7.38 x 10(-10) cm(2)s(-1)) and potassium (KCl 2M, 1.05 x 10(-9) cm(2)s(-1)). Moreover, the complete mitigation of the crossover of redox species with higher molecular sizes than the ions from alkali metal salts was confirmed by using in-line benchtop NMR methods. Additionally, the modified PIM membranes were measured in a symmetric electrochemical flow cell using an aqueous electrolyte by combining lithium ferro/ferricyanide redox compounds and lithium chloride. The electrochemical tests showed low polarization, high-rate capability, and capacity retention values of 99% when cycled at 10 mAcm(-2) for over 50 cycles. Based on these results, these polymers could be used as highly selective and conducting membranes in electrodialysis for lithium separation and lithium-based redox flow batteries and as a protective layer in high-energy density lithium metal batteries.

A good integration of the polymer materials that form a mixed-matrix membrane (MMM) for gas separation is essential to reaching interesting permselective properties. In this work, a porous polymer network (PPN), obtained by combining triptycene and trifluoroacetophenone, has been used as a filler, which was blended with two o-hydroxypolyamides (HPAs) that act as polymer matrices. These polymer matrices have been thermally treated to induce a thermal rearrangement (TR) of the HPAs to polybenzoxazoles (β-TR-PBOs) through a solid-state reaction. For its structural study, various techniques have been proposed that allow us to undertake a morphological investigation into the integration of these materials. To access the internal structure of the MMMs, three different methods were used: a polishing process for the material surface, the partial dissolution of the polymer matrix, or argon plasma etching. The argon plasma technique has not only revealed its potential to visualize the internal structure of these materials; it has also been proven to allow for the transformation of their permselective properties. Force modulation and phase contrast in lift-mode techniques, along with the topographic images obtained via the tapping mode using a scanning probe microscope (SPM), have allowed us to study the distribution of the filler particles and the interaction of the polymer and the filler. The morphological information obtained via SPM, along with that of other more commonly used techniques (SEM, TGA, DSC, FTIR, WASX, gas adsorption, and permeability measurements), has allowed us to postulate the most probable structural configuration in this type of system.

Despite exhibiting excellent thermal/chemical stability, mechanical robustness, and easy processability, which makes them attractive candidates for gas separation applications, aromatic polyimides are susceptible to plasticization. This study proposes an effective approach to suppress CO2-induced plasticization in a high fractional free volume (FFV) polyimide (PI*) derived from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 2,4,6trimethylphenyldiamine. PI* was first modified by incorporating 3,5-diaminobenzoic acid (DABA) and polyethylene oxide segments (PEO) into the polymer backbone, with the goal of partially removing PEO through high temperature (450 degrees C) pyrolysis, thereby increasing the membrane FFV and, simultaneously, providing enhanced plasticization resistance via DABA cross-linking. To mitigate the effects of themomechanical history, the membranes were aged prior to the thermal treatment process. However, the great enhancement in plasticization resistance was not accompanied by a parallel improvement in the separation performance relative to PI*. To address this shortcoming, a microporous organic polymer (POP) was blended with the polyimides to fabricate mechanically-robust mixed matrix membranes (MMMs). Remarkably, MMM plasticization was suppressed even without the aid of thermal crosslinking for PEO-containing PI*, which was rationalized by molecular simulation invoking the formation of hydrogen bonds between the lactam groups of the POP and PEO moieties.

Microporous glassy polymer membranes suffer from physical aging, which adversely affects their performance in the short time frame. We show that the aging propensity of a model microporous polymer, poly(1-trimethylsilyl-1-propyne) (PTMSP), can be effectively mitigated by blending with as little as 5 wt % porous polymer network (PPN) composed of triptycene and isatin. The aging behavior of these materials was monitored via N2 pure gas permeability measurements over the course of 3 weeks, showing a 14% decline in PTMSP blended with 5 wt % PPN vs a 41% decline in neat PTMSP. Noteworthy, PPNs are 2 orders of magnitude cheaper than the porous aromatic frameworks previously used to control PTMSP aging. A variety of experimental and computational techniques, such as Positron Annihilation Lifetime Spectroscopy (PALS), free volume measurements, cross-polarization/magic angle spinning (CP/MAS) 13C NMR, transport measurements and molecular dynamics (MD) simulations were used to uncover the molecular mechanisms leading to enhanced aging resistance. We show that partial PTMSP chain adsorption into the PPN porosity reduces the PTMSP local segmental mobility, leading to improved aging resistance. Permeability coefficients were broken into their elementary sorption and diffusion contributions, to elucidate the mechanism by which the reduced PTMSP local segmental mobility affects selectivity in gas separation applications. Finally, we demonstrate that in these systems, where both chemical and physical interactions take place, transport coefficients must be corrected for thermodynamic nonidealities to avoid erroneous interpretation of the results.

Mixed matrix membranes (MMMs) provide the opportunity to test new porous materials in challenging applications. A series of low-cost porous organic polymer (POPs) networks, possessing tunable porosity and high CO2 uptake, has been obtained by aromatic electrophilic substitution reactions of biphenyl, 9,10-dihydro-9,10-dimethyl-9,10-ethanoanthracene (DMDHA), triptycene and 1,3,5-triphenylbenzene (135TPB) with dimethoxymethane (DMM). These materials have been characterized by FTIR, 13C NMR, WAXD, TGA, SEM, and CO2 uptake. Finally, different loadings of these POPs have been introduced into Matrimid, Pebax, and chitosan:polyvinyl alcohol blends as polymeric matrices to prepare MMMs. The CO2/CH4 separation performance of these MMMs has been evaluated by single and mixed gas permeation experiments at 4 bar and room temperature. The effect of the porosity of the porous fillers on the membrane separation behavior and the compatibility between them and the different polymer matrices on membrane design and fabrication has been studied by Maxwell model equations as a function of the gas permeability of the pure polymers, porosity, and loading of the fillers in the MMMs. Although the gas transport properties showed an increasing deviation from ideal Maxwell equation prediction with increasing porosity of the POP fillers and increasing hydrophilicity of the polymer matrices, the behavior of biopolymer-based CS:PVA MMMs approached that of Pebax-based MMMs, giving scope to not only new filler materials but also sustainable polymer choices to find a place in membrane technology.

A new set of microporous organic polymers (POPs) containing diphosphine derivatives synthesized by knitting via Friedel–Crafts has been attained. These amorphous three-dimensional materials have been prepared by utilizing diphosphines, 1,3,5-triphenylbenzene, and biphenyl as nucleophile aromatic groups, dimethoxymethane as the electrophilic linker, and FeCl3 as a promoting catalyst. These polymer networks display moderate thermal stability and high microporosity, boasting BET surface areas above 760 m2/g. They are capable of coordinating with palladium acetate, using the phosphine derivative as an anchoring center, and have proven to be highly efficient catalysts in Suzuki–Miyaura coupling reactions involving bromo- and chloroarenes under environmentally friendly (using water and ethanol as solvents) and aerobic conditions. These supported catalysts have achieved excellent turnover numbers (TON) and turnover frequencies (TOF), while maintaining good recyclability without significant loss of activity or Pd leaching after five consecutive reaction cycles.

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.

By employing a variation of the polyamidation method using in situ silylated diamines and acid chlorides, it was possible to obtain a rod-type polyamide: poly(p-phenylene terephthalamide) (PPTA, a polymer used in the high-value-added material Kevlar), with a molecular weight much higher than that obtained with the classical and industrial polyamidation method. The optimization of the method has consisted of using, together with the silylating agent, a mixture of pyridine and a high-pKa tertiary amine. The research was complemented by a combination of nuclear magnetic resonance and molecular simulation studies, which determined that the improvements in molecular weight derive mainly from the formation of silylamide groups in the growing polymer.

A set of linear polymers were synthesized utilizing an electrophilic aromatic substitution reaction (SEAr) between biphenyl and ketone containing electron-withdrawing groups (isatin, IS; N-methylisatin, MeIS; and 4,5-diazafluoren-9-one, DF). Optimization of the polycondensation reaction was made to obtain high molecular weight products when using DF, which has not previously been used for linear polymer synthesis. Due to the absence of chemically labile units, these polymers exhibited excellent chemical and thermal stability. Linear SEAr polymers were blended with porous polymer networks derived from IS and MeIS, and both neat/mixed materials were tested as membranes for gas separation. The gas separation properties of both pristine polymers and mixed matrix membranes were good, showing some polymer membrane CO2 permeability values higher than 200 barrer.

A set of aromatic copolyimides was obtained by reaction of 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), and mixtures of the diamines 1,4-bis(4-amino-2-trifluoromethylphenoxy)-2,5-di-tert-butylbenzene (CF3TBAPB) and 3,5-diamino benzoic acid (DABA). These polymers were characterized and compared with the homopolymer derived from 6FDA and CF3TBAPB. All copolyimides showed high molecular weight values and good mechanical properties. The presence of carboxylic groups in these copolymers allowed their chemical crosslinking by reaction with 1,4-butanediol. Glass transition temperatures (Tg) were higher than 260 °C, showing the non-crosslinked copolyimides had the highest Tg values. Degradation temperature of crosslinked copolyimides was lower than their corresponding non-crosslinked ones. Mechanical properties of all polymers were good, and thus, copolyimide (precursor, and crosslinked ones) films could be tested as gas separation membranes. It was observed that CO2 permeability values were around 100 barrer. Finally, the plasticization resistance of the crosslinked material having a large number of carboxylic groups was excellent.

A set of thermally rearranged mixed matrix membranes (TR-MMMs) was manufactured and tested for gas separation. These membranes were obtained through the thermal treatment of a precursor MMM with a microporous polymer network and an o-hydroxypolyamide,(HPA) created through a reaction of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (APAF) and 5′-terbutil-m-terfenilo-3,3″-dicarboxylic acid dichloride (tBTmCl). This HPA was blended with different percentages of a porous polymer network (PPN) filler, which produced gas separation MMMs with enhanced gas permeability but with decreased selectivity. The thermal treatment of these MMMs gave membranes with excellent gas separation properties that did not show the selectivity decreasing trend. It was observed that the use of the PPN load brought about a small decrease in the initial mass losses, which were lower for increasing PPN loads. Regarding the glass transition temperature, it was observed that the use of the filler translated to a slightly lower Tg value. When these MMMs and TR-MMMs were compared with the analogous materials created from the isomeric 5′-terbutil-m-terfenilo-4,4″-dicarboxylic acid dichloride (tBTpCl), the permeability was lower for that of tBTmCl, compared with the one from tBTpCl, although selectivity was quite similar. This fact could be attributed to a lower rigidity as roughly confirmed by the segmental length of the polymer chain as studied by WAXS. A model for FFV calculation was proposed and its predictions compared with those evaluated from density measurements assuming a matrix-filler interaction or ideal independence. It turns out that permeability as a function of FFV for TR-MMMs follows an interaction trend, while those not thermally treated follow the non-interaction trend until relatively high PPN loads were reached.

Copoly(o-hydroxyamide)s (HPA) and copoly(o-hydroxyamide-amide)s (PAA) have been synthesized to be used as continuous phases in mixed matrix membranes (MMMs). These polymeric matrices were blended with different loads (15 and 30 wt.%) of a relatively highly microporous porous polymer network (PPN). SEM images of the manufactured MMMs exhibited good compatibility between the two phases for all the membranes studied, and their mechanical properties have been shown to be good enough even after thermal treatment. The WAX results show that the addition of PPN as a filler up to 30% does not substantially change the intersegmental distance and the polymer packing. It seems that, for all the membranes studied, the free volume that determines gas transport is in the high end of the possible range. This means that gas flow occurs mainly between the microvoids in the polymer matrix around the filler. In general, both HPA- and PAA-based MMMs exhibited a notable improvement in gas permeability, due to the presence of PPN, for all gases tested, with an almost constant selectivity. In summary, although the thermal stability of the PAA is limited by the thermal stability of the polyamide side chain, their mechanical properties were better. The permeability was higher for the PAA membranes before their thermal rearrangement, and these values increased after the addition of moderate amounts of PPN.