Pervaporation and gas separation performances of polymer membranes can be improved by crosslinking or addition of metal-organic frameworks (MOFs). Crosslinked copolyimide membranes show higher plasticization resistance and no significant loss in selectivity compared to non-crosslinked membranes when exposed to mixtures of CO2/CH4 or toluene/cyclohexane. Covalently crosslinked membranes reveal better separation performances than ionically crosslinked systems. Covalent interlacing with 3-hydroxypropyldimethylmaleimide as photocrosslinker can be investigated in situ in solution as well as in films, using transient UV/Vis and FTIR spectroscopy. The photocrosslinking yield can be determined from the FTIR-spectra. It is restricted by the stiffness of the copolyimide backbone, which inhibits the photoreaction due to spatial separation of the crosslinker side chains. Mixed-matrix membranes (MMMs) with MOFs as additives (fillers) have increased permeabilities and often also selectivities compared to the pure polymer. Incorporation of MOFs into polysulfone and Matrimid® polymers for MMMs gives defect-free membranes with performances similar to the best polymer membranes for gas mixtures, such as O2/N2 H2/CH4, CO2/CH4, H2/CO2, CH4/N2 and CO2/N2 (preferentially permeating gas is named first). The MOF porosity, its particle size and content in the MMM are factors to influence the permeability and the separation performance of the membranes.

Aggregates of a lipophilic guanine (G) derivative have been studied in n-hexane by femtosecond-to-microsecond UV-visible broadband transient absorption, stationary infrared and UV-visible spectroscopy and by quantum chemical calculations. We report the first time-resolved spectroscopic detection of hydrogen transfer in GG aggregates, which leads to (G-H)(·) radicals by means of G(+)G(-) charge transfer followed by proton transfer. These radicals show a characteristic electronic spectrum in the range 300-550 nm. The calculated superimposed spectrum of the species that result from NH⋅⋅⋅N proton transfer agrees best with the experimental spectrum.

BACKGROUND: Photo‐crosslinkable polymers are well known and commercially applied as photoresists. But so far they have not been applied as membrane materials for separation processes. They would offer certain advantages in membrane fabrication over conventional crosslinked polymer materials. Therefore, in this work, a poly[ethene‐stat‐(methacrylic acid)] (PEMAA) which is a potential membrane polymer for different separation problems was functionalised with photo‐crosslinkable maleimide side groups. RESULTS: It has been shown that PEMAA can be used as basic polymer material and a conversion with 3‐hydroxypropylmaleimide is possible in order to obtain a photo‐crosslinkable polymer. Investigation of the crosslinking mechanism was performed using stationary infrared and UV‐visible spectroscopy as well as nanosecond transient spectroscopy absorption measurements of a rotating film. Intense transient absorption of the maleimide‐esterified PEMAA occurs at 250 nm in the film pointing to maleimide anion formation and crosslinking via an ionic dimerisation mechanism. CONCLUSION: It is found that crosslinking reactions can be observed spectroscopically in situ using a maleimide‐functionalised PEMAA. Furthermore, experiments can be performed in the liquid phase (polymer in solution) as well as in the solid phase (polymer film) using a rotating polymer film sample. Maleimide anion formation and crosslinking via an ionic dimerisation mechanism can be investigated by variation of the polymer structure as well as the structure of the maleimide side groups. Copyright © 2009 Society of Chemical Industry

A series of new imine‐bridged dicatechol ligands 3a–f‐H4 with sterically demanding groups at the spacers are used for the formation of titanium(IV) complexes M4[(3)3Ti2]. All three ligands 3a–c‐H4 form triple‐stranded dinuclear helicates. When the bulky ligands 3a‐H4 or 3c‐H4 are used with potassium as the countercation, oligomeric or polymeric side products are also observed. The imine‐bridged ligand 3e‐H4 quantitatively forms helicates M4[(3e)3Ti2] and not a M4L6 tetrahedron as observed with Raymond’s analogous amide‐bridged dicatechol ligand 3i‐H4. NMR spectroscopic investigations at variable temperature show that ligand 3f‐H4, which possesses a spiro fluorenyl group at the central unit of the spacer, forms the meso‐helicate M4[(3f)3Ti2]. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)