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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

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.

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.