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Spirobichroman-based polymers with high gas permeability and selectivity are promising for their applications as membranes in gas separation. In this study, three spirobichroman-based polyimides (PIs; 6FDA-FH, 6FDA-DH, and 6FDA-MH) were synthesised by the polyreaction between diamines containing different substituents (benzene ring, pyridine ring, and methyl group) and 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA). The physical properties, gas transport behaviour, d-spacing, dihedral angle of molecules, and fractional free volume of the PIs were investigated through experiments and molecular simulations. The PIs exhibited excellent thermal stability and good solubility in common organic solvents. The gas permeability of the PIs was investigated; the results highlighted the critical role of the substituents in the enhancement of the gas separation performance of polymer membranes. Detailed analysis of the PIs showed that 6FDA-FH exhibits the highest gas permeability. This can be ascribed to the loose packing of the polymer chain owing to the increased dihedral angle between the two planes. However, the methyl substituent in 6FDA-MH disrupts the polymer chain packing rather than changing the dihedral angle between the two planes, thus enhancing the gas permeability of 6FDA-MH. Furthermore, 6FDA-DH exhibited the highest CO2/CH4 selectivity, which is attributed to the CO2 affinity of the polymer containing the pyridine unit.

Electrochromic (EC)/electrofluorochromic (EFC) bifunctional materials are receiving great attention because of their promising applications in optoelectronic devices. However, the development of ideal EC/EFC bifunctional materials is still a great challenge because of the poor integration of EC/EFC performances (optical contrast, response speed, and switching stability). Herein, we reported two novel diphenylamine-based mixed valence (MV) polyamides (S-HPA and P-HPA) with spirobifluorene (2,7-positions) and pyrene (1,6-positions) as bridged fluorescence units, respectively, showing impressive cyclability and fluorescence contrast with rapid switching. Through the formation of an effective electronic coupling between the two nitrogen centers using spirobifluorene/pyrene bridges, we demonstrated that different bridges have significant effects on the thermal and electrooptical characteristics of polyamides. In addition to lower fluorescence quantum yield and glass transition temperature, the S-HPA exhibited superior cyclability (contrast change

In this study, carboxyl potassium salt polysulfone PSF-COOK60% was selected as an additive and carboxylated polysulfone PSF-COOH60% was identified as a membrane matrix material to prepare mixed matrix membranes via a traditional phase separation method. The viscosity of the casting solutions, as well as the electronegativity, hydrophilicity, and morphologies of the mixed matrix membranes, greatly changed with the addition of PSF-COOK60%. This was because -COOK was more easily ionized than -COOH into -COO−, which affected the charges, conformations, and hydrophilicity of the polymer chains. In particular, the membrane with a PSF-COOK60%:PSF-COOH60% ratio of 3:7 (M3) exhibited a minimum aperture of 1.825 nm and a maximum electronegativity of −29.9 mV. M3 offered outstanding separation efficiency of dye/salt mixtures as seen in the rejection rates of Congo red (as high as 95.5%) and organic salts (as low as 5.6%), as well as the pure water flux of 153.8 L/m2·h·bar. Furthermore, M3 had excellent anti-dye-fouling performance and showed wide application conditions. Therefore, M3 is an ideal candidate for separation membranes for the fractionation of dye/salt mixtures. The PSF-COOK and other polymer carboxylates can be used as a new kind of additive to change the morphology and chemical properties of the membranes.

In this work, 4,4′-isopropylidenedicyclohexanol (HBPA)-based dinitro isomers mixture (H″BPBN and H′BPBN) was synthesized and separated, and the structures of dinitro isomers were confirmed by differential scanning calorimetry and proton nuclear magnetic resonance spectroscopy. A series of copolyimides were prepared from diamino monomers with different percentages of novel diamine H″BPDA and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride via a conventional two-step procedure. All the copolyimides could afford flexible, tough, and transparent films with transmittance no less than 73% at 450 nm, which was attributed to the fact that nonplanar alicyclic diamine and the bulky and weakly polarizable trifluoromethyl hampered the formation of charge-transfer complex. Moreover, all the copolyimides were soluble not only in polar solvents such as N,N-dimethylformamide but also in low-boiling-point solvents such as dichloromethane, which was related to the fact that the existence of alicyclic diamine and bulky trifluoromethyl decreased the intermolecular force. In addition, the conformation effects of H″BPDA and H′BPDA on the aspects of thermal, mechanical, optical, and soluble performance of copolyimides were investigated and their structure–property relationships were discussed in detail.

Novel positively charged nanofiltration membranes were facilely prepared by polydopamine (PDA) deposition followed by crosslinking on the polyethersulfone (PES) ultrafiltration (UF) membrane substrate. Specifically, small molecules DMAPA and 1,3-dibromopropane were separately selected as the bridge agent and crosslinking agent, which can not only realize the moderate crosslinking and densification of the loose structure of the PDA layer, but also further improve the hydrophilicity and positive charges of the PDA layer. Under the optimized conditions of DMAPA concentration (2 g/L), 1,3-dibromopropane concentration (10 wt%) and reaction time (9 h), the composite membrane had the surface pore size as low as 1.1 nm, water contact angle as low as 35.1° and zeta potential as high as +63.8 mV at pH = 6. As a result, the optimized positively charged NF membrane (M3) showed an outstanding permeance up to 15.7 L m−2 h−1 bar−1 while maintaining a high rejection above 95% for MgCl2. Meanwhile, M3 also showed good environmental adaptability when facing complex feeding or operating conditions. This work provided new situation in the design and construction of positive charged NF membranes for high efficiency cation separation.

Sulfonated hyperbranched polyethersulfone (SHBPES)-modified halloysite nanotubes (HNTs), HNT-SHBPES, were synthesized and mixed with polyethersulfone (PES) to prepare hybrid ultrafiltration (UF) membranes via the phase inversion method. Pure PES and PES hybrid membranes mixed with SHBPES and HNTs were also prepared. The HNT-SHBPES showed good compatibility with the PES membrane matrix, and a series of PES/HNT-SHBPES hybrid membranes offered improved porosity, surface mean pore size, hydrophilicity, permeability, and anti-fouling properties. These were mainly attributed to the synergistic effects of hydrophilic -SO3H of SHBPES, porous HNTs, and the tiny interspace between HNT-SHBPES and PES matrix. When 8% HNT-SHBPES was doped into PES casting solution (MHS–8), its pure water flux reached 351.6 L/m2 h—this was nearly 2.2 times that of the pure PES membrane (M–0); its rejection rate remained high primarily due to the occurrence of delayed phase separation in the solidification process and the good compatibility between HNT-SHBPES and PES matrix. This resulted in a relatively dense, uniform, and defect-free surface. Additionally, bovine serum albumin (BSA) and humic acid (HA) were chosen as model contaminants to evaluate the anti-fouling properties of all prepared membranes. After multi-cycles UF experiments, MHS–8 retained a higher flux recovery rate and rejection rate than the other membranes confirming its excellent anti-fouling properties and stable overall performance. This work offers a new possibility for hyperbranched polymer-modified nanomaterials to enhance their compatibility with membrane matrix and improve membrane separation performance.

In this work, hydrogenated bisphenol A (HBPA) based dinitro mixed isomers (1a&prime, and 1a) were synthesized and separated via vacuum distillation under the monitor of DSC and 1H NMR. Corresponding diamines (2a&prime, and 2a) were separately polycondensed with five commercial dianhydrides via a two-step thermal imidization to obtain PI-(1&prime, 5&prime, ) and PI-(1-5). All the polyimides could afford flexible, tough, and transparent films, and most of them were readily soluble not only in common polar solvents like DMAc, but also in low boiling point solvents such as chloroform. 1H NMR spectra of the polyimides demonstrated that HBPA moiety showed no conformation changes during the preparation of polymers. For a given dianhydride, PI-(1-5) exhibited better thermal stability than that of PI-(1&prime, ), this can be attributed that the equatorial, equatorial C&ndash, O in PI-(1-5) promoted denser and more regular molecular chain stacking, as can be evidenced by the WAXD and geometric optimization results. Additionally, when the dianhydride was ODPA, BPADA or 6FDA, no apparent difference was found in either the transmittance or solubility between two series of polyimides, which could be attributed that twisted and flexible ether linkages, as well as bulky substituents, led to the &ldquo, already weakened&rdquo, inter- and intramolecular CT interaction and cohesive force. However, when it came to rigid and stiff dianhydride, e.g., BPDA, PI-3&prime, took an obvious advantage over PI-3 in transmittance and solubility, which was possibly owed to the larger molecular chain d-spacing imparted by equatorial, axial C&ndash, O. An overall investigation of PI-(1&prime, ) and PI-(1-5) on aspects of thermal, mechanical, morphological, soluble and optical performance values was carried out, and the conformation effects of HBPA isomers on the properties of two series of polyimides were discussed in detail.

In this work, hydrogenated bisphenol A (HBPA) based dinitro mixed isomers (1a′ and 1a) were synthesized and separated via vacuum distillation under the monitor of DSC and 1H NMR. Corresponding diamines (2a′ and 2a) were separately polycondensed with five commercial dianhydrides via a two-step thermal imidization to obtain PI-(1′-5′) and PI-(1-5). All the polyimides could afford flexible, tough, and transparent films, and most of them were readily soluble not only in common polar solvents like DMAc, but also in low boiling point solvents such as chloroform. 1H NMR spectra of the polyimides demonstrated that HBPA moiety showed no conformation changes during the preparation of polymers. For a given dianhydride, PI-(1-5) exhibited better thermal stability than that of PI-(1′-5′), this can be attributed that the equatorial, equatorial C–O in PI-(1-5) promoted denser and more regular molecular chain stacking, as can be evidenced by the WAXD and geometric optimization results. Additionally, when the dianhydride was ODPA, BPADA or 6FDA, no apparent difference was found in either the transmittance or solubility between two series of polyimides, which could be attributed that twisted and flexible ether linkages, as well as bulky substituents, led to the “already weakened” inter- and intramolecular CT interaction and cohesive force. However, when it came to rigid and stiff dianhydride, e.g., BPDA, PI-3′ took an obvious advantage over PI-3 in transmittance and solubility, which was possibly owed to the larger molecular chain d-spacing imparted by equatorial, axial C–O. An overall investigation of PI-(1′-5′) and PI-(1-5) on aspects of thermal, mechanical, morphological, soluble and optical performance values was carried out, and the conformation effects of HBPA isomers on the properties of two series of polyimides were discussed in detail.

Supplemental Material, Revised_supporting_information for Soluble copolyimides containing 4,4′-isopropylidenedicyclohexanol (HBPA) isomer units: Synthesis, characterization, thermal, mechanical, and optical properties by Ziwen Hou, Sizhuo Jin, Xiaowen Wang, Shuai Wang, Junyu Zhao, Zhiming Mi, Shengqi Ma, Daming Wang, Xiaogang Zhao, Hongwei Zhou and Chunhai Chen in High Performance Polymers

Poly (ether sulfone) (PES), as a kind of special engineering plastic, is widely used in the field of separation. However, its gas separation performance is unremarkable. Therefore, a series of PES containing the tetraphenyl bipyrimidine unit (PES-TPhbpy-x) was prepared by nucleophilic polycondensation to improve the gas separation performance of PES. PES-TPhbpy-x exhibited a high molecular weight, excellent mechanical properties, and could form robust membranes. With increasing TPhbpy unit content in PES-TPhbpy-x, the glass transition temperature and heat resistance increased. WAXD analysis revealed that the d-spacing of PES-TPhbpy-x is larger than that of PES. This indicated that the TPhbpy unit could hinder the polymer chain packing and enhance the rigidness of the polymers. Compared with PES, PES-TPhbpy-x exhibited an excellent gas separation performance. The CO2 permeability of the PES-TPhbpy-100 increased by 570%, and the CO2/N2 selectivity and CO2/CH4 selectivity increased by 49% and 50%, respectively. Moreover, PES-TPhbpy-100 could form a membrane by the hot-press method. The CO2 permeability of the PES-TPhbpy-100 membrane prepared by the hot-press method was 12.81 barrer. In addition, the CO2/N2 and CO2/CH4 selectivities were 32.0 and 37.7, which were 27% and 35% higher than those of the PES membrane, respectively.

Four spirobichroman-based polyimides (6FDA-F, 6FDA-O, 6FDA-P, and 6FDA-M) were successfully obtained via polyreaction between diamines of different substituents (-H, -OCH3, -N, and -CH3) and 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA). The molecular weights, thermophysical, dihedral angle of the molecules, fractional free volume, d-spacing, Brunauer–Emmett–Teller surface area, and gas separation performance were studied through a combination of experiments and molecular dynamics simulations. These polymers show high molecular weights, with number-average molecular weights (Mn) in the range of 5.0–15.3 × 104, and excellent thermal stability, with weight loss temperatures (T5%) of over 420 °C. The pure-gas (O2, N2, CO2, and CH4) permeation results indicated that the four polymers selectivity of CO2/CH4 over 31 and that 6FDA-F had the highest gas permeability among the four tested gases. Importantly, the dihedral angle from molecular simulation was used to clarify the phenomenon wherein the 6FDA-P gas permeability lower than 6FDA-F. A detailed analysis indicates that -CH3 increased the gas permeability of the polyimides, while the turnstile-like rotary thermal motion of -OCH3 formed channel obstacles and improved the gas selectivity. The polymers containing pyridine ring and those containing benzene ring follows different gas separation mechanisms, based on the gas solution-diffusion behaviour.