A novel series membranes based on non-linear all-aromatic polyimides (PIs) was investigated with the aim to understand how the PI backbone geometry and local electrostatics govern gas transport and the ability to separate CO₂/CH₄ mixtures. Non-linear 3-ring aromatic diamines, with exocyclic bond angles varying between 120 and 134°, enable the design of high Tg (>276 °C) PIs. A polar 1,3,4-oxadiazole diamine (ODD) (μ = 3D) monomer and a non-polar m-terphenyl diamine (TPD) reference monomer were synthesized and coupled with 3 dianhydrides, i.e. ODPA, ODDA, and 6FDA. In 6FDA-based membranes CO₂ permeabilities (P_CO2) are the highest of the series. The 6FDA-ODD membrane shows excellent membrane performance with high P_CO2 values at all feed pressures. Up to 12 bar (6 bar CO₂) none of the membranes reached their plasticization pressure. The non-linear backbone geometry promotes CO₂ permeability, whereas the presence of an electrostatic dipole moment associated with the 1,3,4-oxadiazole heterocycle governs CO₂/CH₄ separation selectivity.

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We report on the morphology and mechanical properties of nanocomposite films derived from aqueous, hybrid liquid crystalline mixtures of rodlike aggregates of a sulfonated, all-aromatic polyamide, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT), and graphene oxide (GO) platelets. An isothermal step at 200 °C facilitates in situ partial thermal reduction of GO to reduced GO (rGO) in nanocomposite films. X-ray scattering studies reveal that PBDT-rGO nanocomposites exhibit both higher in-plane alignment of PBDT (the order parameter increases from 0.79 to 0.9 at 1.8 vol % rGO) and alignment along the casting direction (from 0.1 to 0.6 at 1.8 vol % rGO). From dynamic mechanical thermal analysis, the interaction between PBDT and rGO causes the β-relaxation activation energy for PBDT to increase with rGO concentration. Modulus mapping of nanocomposites using atomic force microscopy demonstrates enhanced local stiffness, indicating reinforcement. From stress-strain analysis, the average Young's modulus increases from 16 to 37 GPa at 1.8 vol % rGO and the average tensile strength increases from 210 to 640 MPa. Despite polymer alignment along the casting direction, an average transverse tensile strength of 230 MPa is obtained.

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Thermoplastic polyaryletherketones (PAEKs) exhibit excellent mechanical properties and fluid stability, but their glass transition temperatures (Tg) are low and their all-aromatic nature makes processing challenging. We will present a synthetic route toward phenylethynyl-functionalized hyperbranched PAEKs (hbPAEKs) (Tg = 151 °C) that can be cross-linked to form flexible films with high Tg's (187-237 °C) and good mechanical properties (E′ = 4 GPa, σ = 44 MPa, and ϵ = 1.76%). After cross-linking, the films are amorphous, easy to handle, and insoluble. We will report on the melt rheology of the hbPAEK precursors, with and without reactive phenylethynyl-reactive functionalities, and the thermomechanical characteristics of thin cross-linked films using dynamic mechanical thermal analysis, differential scanning calorimetry, and tensile testing. We believe that our findings can be extended to other all-aromatic structural and functional polymer architectures that are otherwise impossible to process.

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Combining polymers with small amounts of stiff carbon-based nanofillers such as graphene or graphene oxide is expected to yield low-density nanocomposites with exceptional mechanical properties. However, such nanocomposites have remained elusive because of incompatibilities between fillers and polymers that are further compounded by processing difficulties. Here we report a water-based process to obtain highly reinforced nanocomposite films by simple mixing of two liquid crystalline solutions: a colloidal nematic phase comprised of graphene oxide platelets and a nematic phase formed by a rod-like high-performance aramid. Upon drying the resulting hybrid biaxial nematic phase, we obtain robust, structural nanocomposites reinforced with graphene oxide.

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A homologous series of 12 all-aromatic PEI membranes was investigated with the aim to understand how subtle changes in the PEI main-chain affect the carbon dioxide/methane (CO₂/CH₄) gas separation performance. The 3-ring diamines selected for this study are either para-, meta- or ortho-aryloxy substituted with respect to the central benzene ring, i.e. 1,4-bis(4-aminophenoxy)benzene (P1), 1,3-bis(4-aminophenoxy)benzene (M1) and 1,2-bis(4-aminophenoxy)benzene (O1). Doing so changes the backbone geometry from a more linear to a more kinked conformation. In addition, four dianhydrides were selected with the aim to tailor the segmental mobility and hence the free volume of the PEIs, i.e. pyromellitic dianhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and 3,3′,4,4′-oxydiphthalic dianhydride (ODPA). We have investigated how subtle changes in these prototypical PEIs affect membrane critical performance criteria such as CO₂ permeability, CO₂/CH₄ selectivity and ability to withstand high operating pressures. In ODPA-based membranes the CO₂ permeability decreases in the order P1 > O1 > M1 and remains steady throughout measurements with mixed feed pressures up to 40 bar, however, the selectivity decreases for ODPA-O1 and ODPA-M1. For high-pressure applications, the OPDA-P1 membrane is a good candidate with a selectivity of 48, permeability of CO₂ of 0.74 Barrer and ability to resist plasticization up to 40 bar of total pressure (16 bar of CO₂ partial pressure). Alternatively, for applications up to 10 bar of total mixed feed (5 bar of CO₂ partial pressure), BPDA-O1 is a promising candidate because this membrane displays a high selectivity of 70 and permeability of 1.3 Barrer.

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In this paper we will describe the synthesis and properties of two series of high molecular weight segmented block copolymers from all-aromatic amorphous (AM) or liquid crystal (LC) telechelic ester-based maleimide-functionalized oligomers (M_n = 5 kg mol^-1) and telechelic thiol-terminated poly(dimethylsiloxane) (PDMS, M_n = 1, 5 and 10 kg mol^-1). The multiblock copolymers were prepared via highly efficient thiol-ene click chemistry, and have M_ns ranging from 22 to 58 kg mol^-1. The segmented block copolymers prepared from mesogenic (LC) units show micro-phase separation and liquid crystallinity even with a PDMS content as high as 65 wt%. The AM5K-based series is completely amorphous. The multiblock copolymers with PDMS5K and 10K show two T_gs at ∼-120 °C and ∼120 °C, respectively, implying the presence of a (micro)phase separated system. The multiblock copolymer prepared from AM5K and PDMS1K displays excellent stress-strain behavior at 25 °C, with a tensile strength of 123.6 MPa, an elastic modulus of 3.4 GPa, an elongation at break of 31.2% and toughness of 30.7 MJ m^-3. The LC5K based multiblock copolymer films exhibit poor stress-strain behavior, which is the result of a higher degree of phase separation and low phase intermixing, as confirmed by TEM measurements. The shape memory properties of the PDMS-containing segmented block copolymers in the temperature range of -150 to 150 °C were tested using a rheometer in torsion mode. The glass transitions originating from the rigid aromatic blocks and flexible PDMS blocks were used as the reversible switches for designing T_g-based dual- and triple-shape memory polymer films. The AM5K-b-PDMS1K and LC5K-b-PDMS1K multiblock copolymers show dual-shape memory behavior in the temperature range of 20-150 °C. The PDMS5K based analogs show triple shape-memory behavior in the temperature range of -150-150 °C.

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The reaction kinetics and structure property relationships of isomeric tri-aromatic ether-linked amines based on the structure bis (aminophenoxy) benzene, cured with diglycidyl ether of bisphenol F (BisF) are investigated in this study. Reaction kinetics are explored using rheological and calorimetric measurements, whereas structure property relationships are determined from their flexural properties, dynamic mechanical properties (DMTA), and thermogravimetric analysis (TGA). A BisF network cured with 4,4 diamino diphenyl sulphone (44 DDS) is used as a benchmark to represent a commercially available high-performance resin system. Varying the substitution of the ether linkages on the aromatic groups from ortho, meta to para was found to have a significant impact on reactivity and network properties after cure. The variations are explained in terms of inductive and resonance effects primarily acting on the outer aromatic rings. Interestingly, however, these same effects acting on the central aromatic ring also impact upon reactivity despite their proximity from the amines. Mechanical and thermal properties are explained by changes in the short-range molecular mobility within the network architecture such as phenylene rotations or π flips and are experimentally validated from the breadth and position of the subambient γ relaxations.@en

The ubiquitous biomacromolecule DNA has an axial rigidity persistence length of ~50 nm, driven by its elegant double helical structure. While double and multiple helix structures appear widely in nature, only rarely are these found in synthetic non-chiral macromolecules. Here we report a double helical conformation in the densely charged aromatic polyamide poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) or PBDT. This double helix macromolecule represents one of the most rigid simple molecular structures known, exhibiting an extremely high axial persistence length (~1 micrometer). We present X-ray diffraction, NMR spectroscopy, and molecular dynamics (MD) simulations that reveal and confirm the double helical conformation. The discovery of this extreme rigidity in combination with high charge density gives insight into the self-assembly of molecular ionic composites with high mechanical modulus (~ 1 GPa) yet with liquid-like ion motions inside, and provides fodder for formation of other 1D-reinforced composites.@en

Tri-aryl ether and ketone amine isomers with varying meta and para aromatic substitution have been cured with a commercially available diglycidyl ether of bisphenol F epoxy resin. The mechanical and thermal properties, as well as reaction rates have been characterised and are related to specific changes in the aryl linkage groups and substitution patterns. In the case of the rate of reaction, inductive and resonance effects, from the strongly electron donating ether groups increase amine reactivity while conversely the electron withdrawing carbonyl groups reduce amine reactivity. With respect to thermal and mechanical properties, comparative molecular mobility within the rigid networks controls the mechanical and thermal properties. The carbonyl group increases Tg, char yield, modulus and strength, whilst reducing displacement at yield. Regardless of chemical linkage, increasing para substitution increased Tg and displacement at failure, whilst reducing strength and stiffness. The insights gained from this work, provide new pathways towards the rational design of a new generation of epoxy amine networks with improved processability, strength, stiffness and ductility.

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Isomeric tri-aryl ketone amines, 1,3-bis(3-aminobenzoyl)benzene (133 BABB), 1,3-bis(4-aminobenzoyl)benzene (134 BABB), and 1,4-bis(4-aminobenzoyl)benzene (144 BABB) are synthesized and cured with diglycidyl ether of bisphenol A and diglycidyl ether of bisphenol F in this work. Differential scanning calorimetry and near-infrared spectroscopy reveal higher rate constants and enhanced secondary amine conversion with increasing para substitution attributed to resonance effects and the electron withdrawing nature of the carbonyl linkages. Glass transition temperatures increase from 133 BABB to 134 BABB, but decrease modestly for the 144 BABB hardener. With increasing para substitution, the flexural modulus and strength both decrease while the strain to failure increases but all BABB amines displaying higher mechanical properties than the corresponding 4,4-diaminodiphenyl sulfone (44 DDS) networks. The thermal stability of the BABB networks is found to be modestly lower than 44 DDS, but char yields are significantly higher. Changes in thermal and mechanical properties are described in terms of molecular structure and equilibrium packing density.

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We have explored semicrystalline poly(decamethylene terephthalamide) (PA 10T) based thermosets as single-component high-temperature (>200 °C) shape memory polymers (SMPs). The PA 10T thermosets were prepared from reactive thermoplastic precursors. Reactive phenylethynyl (PE) functionalities were either attached at the chain termini or placed as side groups along the polymer main chain. The shape fixation and recovery performance of the thermoset films were investigated using a rheometer in torsion mode. By controlling the M_n of the reactive oligomers, or the PE concentration of the PE side-group functionalized copolyamides, we were able to design dual-shape memory PA 10T thermosets with a broad recovery temperature range of 227-285 °C. The thermosets based on the 1000 g mol^-1 reactive PE precursor and the copolyamide with 15 mol % PE side groups show the highest fixation rate (99%) and recovery rate (≥90%). High temperature triple-shape memory behavior can be achieved as well when we use the melt transition (T_m ≥ 200 °C) and the glass transition (T_g = ∼125 °C) as the two switches. The recovery rate of the two recovery steps are highly dependent on the crystallinity of the thermosets and vary within a wide range of 74%-139% and 40-82% for the two steps, respectively. Reversible shape memory events could also be demonstrated when we perform a forward and backward deformation in a triple shape memory cycle. We also studied the angular recovery velocity as a function of temperature, which provides a thermokinematic picture of the shape recovery process and helps to program for desired shape memory behavior.

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The thermoelectric properties of amorphous and semi-crystalline high-performance polyetherimide–SWCNT nanocomposites are reported for the first time. Nanocomposites based on a non-linear polyetherimide (PEI) model system, labeled aBPDA-P3, with 0.6, 4.4 and 10 vol% SWCNTs remained amorphous after the addition of SWCNTs. In contrast, SWCNTs induced crystallization in a linear PEI model system labeled as ODPA-P3. The (thermo)mechanical properties were fully characterized using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMTA). The electrical conductivity was studied by four-probe measurements and showed higher values for the ODPA-P3 films reaching 20 S/m at 10 vol% of SWCNTs. The thermoelectric performance revealed by Seebeck coefficient (S) measurements showed values of 40 and 55 μV/K for the 0.6 and 4.4 vol% ODPA-P3 SWCNT nanocomposites, while 16 and 47 μV/K for aBPDA-P3 amorphous films. This enhancement has been attributed to SWCNT–induced crystallization in ODPA-P3 matrix. The PEI-SWCNT nanocomposites are ideal candidates as organic flexible films and coatings for large area thermal energy harvesting, where high temperature gradients exist. Potential applications can be envisaged in the aerospace, automotive and micro-electronics sectors.

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A star-shaped trifunctional acyl chloride bearing ether linkages was synthesized as an alternative to the commonly used trimesoyl chloride (TMC) in the preparation of polyamide thin film composite membranes (TFC). Although this star-shaped acyl chloride has the same functionality as TMC, it is larger in size and its acyl chloride groups are less reactive due to the electron donating ether linkages. In this work, we prepared TFC membranes by the interfacial polymerization of both this star-shaped acyl chloride and TMC with either one of the two structural isomers: m-phenylenediamine (MPD) or p-phenylenediamine (PPD). No strong effect was observed of the substitution pattern of the aromatic diamine on the membrane formation with TMC, due to the high reactivity of the acyl chloride groups of TMC. In contrast, the use of this star-shaped acyl chloride results in significant differences in the properties of the formed TFC membrane depending on the use of MPD or PPD. Where TMC-MPD membranes are well-known for their excellent retention, we could not obtain defect-free membranes prepared from MPD and this star-shaped triacyl chloride (R_rosebengal<77%). The use of PPD instead of MPD, however, did result in defect-free membranes (R_rosebengal>97%) with an acceptable clean water permeance (2.5 L m⁻² h⁻¹ bar⁻¹).

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We have prepared semi-crystalline polyamide (PA) thermosets using reactive side-group functionalized copolyamides as precursors. Reactive meta- and para-based phenylethynyl diacid chlorides (IPE and TPE) were synthesized and incorporated in poly(decamethylene terephthalamide) (PA 10T) using a low temperature solution polymerization method. The phenylethynyl-based comonomers disrupt crystallization of the final copolyamides and lower the onset of melting. Copolyamides containing 5, 10 and 15 mol% of the reactive comonomer could be cured at 350 °C into freestanding PA thermoset films. All thermoset films are stable up to 400 °C, as confirmed by DMTA, which is the result of network formation. The thermosets exhibit both a crystalline phase and a crosslinked amorphous phase. Depending on the concentration of the side-groups, the degree of crystallinity of the final thermosets can be controlled and suppressed by 52–76% compared to the PA 10T reference polymer. Most notable is the fact that the IPE-15 thermoset film exhibits outstanding stress–strain behavior, i.e. elongation at break (∼17%) and toughness (766 MJ·m⁻³).

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We have synthesized and characterized a new family of nematic all-aromatic polyesteramide thermosets based on 6-hydroxy-2-naphthoic acid (HNA), terephthalic acid (TA), and 4-acetamidophenol (AAP). In order to incorporate a high concentration of the amide-based monomer (AAP), the melt transition (T_K-N) and melt viscosity had to be lowered in order to maintain melt processable intermediates. Precursor thermoplastic reactive oligomers, end-capped with phenylethynyl functionalities, were prepared using standard melt condensation techniques with a target M_n of 1000–9000 g mol⁻¹. The reactive oligomers with 20–30 mol% AAP could easily be processed into films, and the films exhibit good tensile properties in terms of tensile strength (70–80 MPa) and elongation at break (7–10%). A glass transition of 191°C could be obtained when a 1000 g mol⁻¹ oligomer (HNA/TA/AAP(20)–1 K) was thermally cross-linked. When the AAP concentration reaches 35 mol%, the rigidity of the backbone and the hydrogen bonding interactions are enhanced, which make HNA/TA/AAP(35) polymers difficult to process.

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In order to characterize the free volume of a homologous series all-aromatic poly(ether imide) (PEI) membranes, two positron annihilation techniques were utilized: positron annihilation lifetime spectroscopy (PALS) and Doppler broadening (DB) of annihilation radiation. First, DB, which is a fast and convenient method, indicated differences in free volume of all PEIs investigated, whereas PALS experiments gave more quantitative information, with respect to the size and distribution of the voids. DB results show that S, W pairs for this PEI-series tend to group according to their dianhydride moiety, meaning that, in this series, dianhydrides govern the differences in the S parameter, indicating more free volume with increasing S value. The semicrystalline PEI samples exhibit the lowest S parameter, while the amorphous samples based on 3,3′,4,4′-oxydiphthalic dianhydride (ODPA) all lie on the higher S side of the S-W plot. With the 1,4-bis(4-aminophenoxy)benzene (P1)-based PEI (ODPA-P1) standing out with the highest S parameter. The same could be confirmed and quantified by PALS, where ODPA-P1 is the only membrane in this series with its free volume described by both smaller and larger free-volume elements. The larger voids in ODPA-P1 can be characterized as having a radius (R) of 3.3 Å, which is 5 times larger than the lowest measured free-volume content in this series observed for 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 1,3-bis(4-aminophenoxy)benzene (M1)-based PEI (BPDA-M1), which has voids with a radius of R ≈ 0.7 Å. When comparing results obtained by DB and PALS, a very good correlation is observed between the S parameter (determined by DB) and the free-volume content (quantified by PALS).@en

State-of-the-art perovskite-based solar cells employ expensive, organic hole transporting materials (HTMs) such as Spiro-OMeTAD that, in turn, limits the commercialization of this promising technology. Herein an HTM (EDOT-Amide-TPA) is reported in which a functional amide-based backbone is introduced, which allows this material to be synthesized in a simple condensation reaction with an estimated cost of <$5 g⁻¹. When employed in perovskite solar cells, EDOT-Amide-TPA demonstrates stabilized power conversion efficiencies up to 20.0% and reproducibly outperforms Spiro-OMeTAD in direct comparisons. Time resolved microwave conductivity measurements indicate that the observed improvement originates from a faster hole injection rate from the perovskite to EDOT-Amide-TPA. Additionally, the devices exhibit an improved lifetime, which is assigned to the coordination of the amide bond to the Li-additive, offering a novel strategy to hamper the migration of additives. It is shown that, despite the lack of a conjugated backbone, the amide-based HTM can outperform state-of-the-art HTMs at a fraction of the cost, thereby providing a novel set of design strategies to develop new, low-cost HTMs.

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Thermoplastic and thermoset all-aromatic liquid crystal (LC) (AB)_n-multiblock copoly(ester imide)s based on N-(3′-hydroxyphenyl)trimellitimide (IM), 4-hydroxybenzoic acid (HBA), and 6-hydroxy-2-naphthoic acid (HNA) were investigated as single-component high-temperature (≥250 °C) shape memory polymers (SMPs). A high T_g (∼200 °C) HBA/IM block embedded in a low T_g (∼120 °C) HBA/HNA matrix creates a stable rubbery plateau that can be extended to ∼240 °C by cross-linking. The shape fixation (R_f) and shape recovery efficiency (R_r) of the thermoplastic and thermoset films were investigated using a rheometer in torsion mode. Thermoplastic LC copoly(ester imide) films showed excellent dual SM behavior (R_f and R_r ∼ 100%) at 170 °C. After cross-linking the thermoplastic films a single component system as obtained that exhibited high-temperature (≥250 °C) tunable triple SM and one-way reversible SM behavior.

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A series all-aromatic poly(esterimide)s with different molar ratios of N-(3′-hydroxyphenyl)-trimellitimide (IM) and 4-hydroxybenzoic acid (HBA) (IM/HBA = 0.3/0.7 and 0.7/0.3) was prepared with the aim to design flexible high T_g films. Melt-pressed films, either from high molecular weight polymer or cured phenylethynyl precursor oligomers, exhibit T_gs in the range of 200 °C to 242 °C and are brittle. After a thermal stretching procedure, the films became remarkably flexible and very easy to handle. In addition, the thermally stretched 3-IM/7-HBA and 7-IM/3-HBA films show tensile strengths of 108 MPa and 169 MPa, respectively. Thermal treatment increased the T_g of 3-IM/7-HBA from 205 °C to 248 °C, whereas the T_g of 7-IM/3-HBA increased from 230 °C to 260 °C.

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We have explored the synthesis of semi-crystalline polyamide (PA) thermosets via a reactive PA oligomer precursor route. Poly(decamethylene terephthalamide) (PA 10T) oligomers with a target M_n of 1 K and 3 K g·mol⁻¹ were synthesized via solution polymerization and end-capped with reactive phenylethynyl (PE) groups. The reactive oligomers could be cured in a stepwise manner using successive high temperature treatment steps. Depending on the concentration of PE end-groups, the degree of crystallinity of the final thermosets can be controlled and depressed by 60% for the crosslinked 3 K precursor and completely eliminated for the crosslinked 1 K precursor. From the calculated molecular weight between crosslinks, we estimated that 35–41% of the PE end-groups form crosslinking functionalities and the remainder of the PE end-groups contribute to chain extension. All thermoset films are stable up to ∼400 °C in DMTA experiments due to network formation, effectively increase the maximum use temperature of PA 10T by 100 °C.

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