Towards the generalization of membrane structure-property relationship of polyimides and copolyimides: A group contribution study

Molecular Dynamics Simulations of Gas Transport Properties in Cross-Linked Polyamide Membranes: Tracing the Morphology and Addition of Silicate Nanotubes

This study employs molecular dynamics (MD) simulations to fundamentally provide insight into the role of cross-link density in the CO2 separation properties of interfacially polymerized polyamide (PA) membranes. For this purpose, two atomistic models of pure polyamide membranes with different cross-link densities are constructed by MD simulations to conceptually determine how the fractional free volume of polyamide affects the gas separation performance of the membrane. The PA membrane with a lower cross-link density (LCPA) shows a higher gas diffusion coefficient, a lower gas solubility coefficient, and a higher gas permeability than the PA membrane with a higher cross-link density (HCPA). Moreover, the pristine and modified silicate nanotubes (SNTs) as the fast gas transport channels are incorporated into the polyamide membranes to assess the effect of the SNT/PA interface chemistry on the CO2 separation properties of the membranes. SNTs are systematically modified by three modifying agents with different CO2-philic groups and different interfacial interaction energies with the polyamide matrix. The results of MD simulations demonstrate that the incorporation of silicate nanotubes into the PA matrix increases the gas diffusivity and permeability and decreases the CO2/gas selectivity. Moreover, the membranes containing modified SNTs possessing high CO2-philicity and high SNTs/PA interfacial interactions show a high CO2 separation performance.

Preparation of novel diperylene-cored polyimide photocatalyst with broad-spectra response and high stability

A novel polyimide (PI) with broad-spectra response, high photocatalytic activity and stability under super acidic conditions (pH = 0) was synthesized via polymerizing method. Two types of perylene-cored materials (PDIAN and PTCDA) with anhydride and diamine respectively, were applied as precursors for PI polymerization. The as-prepared PI was optimized at 1:1 initial molar ratio of PDIAN to PTCDA. Using common PI (synthesized from melamine and pyromellitic dianhydride) as comparison, the Cr(VI) reduction rate was boosted from 25.4% to 96.6% within 120 min light irradiation. The corresponding rate constant by PI(PDIAN/PTCDA) was estimated to be ca. 11.7 times relative to that by common PI. The boosted performance was ascribed to the strong π-π conjugation from diperylene cores, which can decrease the photoluminescence intensity and electrochemical impedance, so as to promote the separation and transfer of photogenerated electron-hole pairs. In addition, the optimized PI(PDIAN/PTCDA) displayed wide-spectra response, which can still work under 730 nm light. The influencing factors toward Cr(VI) reduction were also clarified to be beneficial at lower pH and increased concentration of hole scavenger. After five cycles at pH 0, the PI still maintained excellent redox activity and structural stability.

Structure-Property Relationship on the Example of Gas Separation Characteristics of Poly(Arylene Ether Ketone)s and Poly(Diphenylene Phtalide)

Three poly(arylene ether ketone)s (PAEKs) with propylidene (C1, C2) and phtalide (C3) fragments, and one phtalide-containing polyarylene (C4), were synthesized. Their chemical structures were confirmed via 1H NMR, 13C NMR and 19F NMR spectroscopy. The polymers have shown a high glass transition temperature (>155 °C), excellent film-forming properties, and a high free volume for this polymer type. The influence of various functional groups in the structure of PAEKs was evaluated. Expectedly, due to higher free volume the introduction of hexafluoropropylidene group to PAEK resulted in higher increase of gas permeability in comparison with propylidene group. The substitution of the fluorine-containing group on a rigid phtalide moiety (C3) significantly increases glass transition temperature of the polymer while gas permeation slightly decreases. Finally, the removal of two ether groups from PAEK structure (C4) leads to a rigid polymer chain that is characterized by highest free volume, gas permeability and diffusion coefficients among the PAEKs under investigation. Methods of modified atomic (MAC) and bond (BC) contributions were applied to estimate gas permeation and diffusion. Both techniques showed reasonable predicted parameters for three polymers while a significant underestimation of gas transport parameters was observed for C4. Gas solubility coefficients for PAEKs were forecasted by "Short polymer chain surface based pre-diction" (SPCSBP) method. Results for all three prediction methods were compared with the ex-perimental data obtained in this work. Predicted parameters were in good agreement with ex-perimental data for phtalide-containing polymers (C3 and C4) while for propylidene-containing poly(arylene ether ketone)s they were overestimated due to a possible influence of propylidene fragment on indices of oligomeric chains. MAC and BC methods demonstrated better prediction power than SPCSBP method.