Characterization of maleimide dimers in photo-cross-linked copolyimide films

Abstract

Copolyimide membranes are established materials for the separation of gaseous and liquid mixtures. Cross-linking of the polymer strands improves the physical and chemical stability. The photo-cross-linking of a 6FDA-ODA/6FDA-DABA 4 : 1 copolyimide membrane containing maleimide side groups as linker was investigated by FTIR spectroscopy. IR absorption spectra of the copolyimide backbone, 3-hydroxypropyldimethyl maleimide and the copolyimide functionalized with 3-hydroxypropyldimethyl maleimide were measured before and after different irradiation times and compared to each other. For band assignment a normal mode analysis was performed. The backbone of the polymer and the maleimide linker can be well distinguished due to their different spectral band positions. Only the films containing a maleimide moiety perform a photoreaction, the polymer backbone does not interfere. Based on the difference spectra and the results of the DFT calculations it was shown that the trans- and the cis-cycloadduct as well as the previously suggested 2-2'-adduct without a cyclobutane ring are formed upon UV irradiation. Evidence for an oxetane-like photoproduct was not found. Different time constants for the increase of the product bands were observed. The cycloadduct accumulates with a shorter time constant (τ = 2 to 5 min) than the 2-2'-adduct (τ = 75 min). The yield of the photo-cross-linking reaction was determined by spectral deconvolution and kinetic fitting of several marker bands. For the copolyimide synthesized in this work, a maximum value of 6% was reached. The stiffness of the copolyimide backbone inhibits further photo-cross-linking.

DNA photoreacts by nucleobase ring cleavage to form labile isocyanates

“…The procedures to obtain these values are described in the ESI. † 44 In the monomer films the isocyanate quantum yields are nearly the same for G and C and for mixed GC. The isocyanate quantum yields in the single oligonucleotide films (dG 10 , dC 10 , dT 10 ) are significantly higher than those obtained for the monomers.…”

Investigation of Cross-Linked and Additive Containing Polymer Materials for Membranes with Improved Performance in Pervaporation and Gas Separation

“…Band positions of negative peaks represent the unshifted positions of the disappearing educts; positive bands can be assigned to those vibrations of the photoproducts, which exhibit different frequencies than the educts. The strong absorption of the polymer backbone is not subject to changes caused by the photoreaction [156] and is thus not visible in the FTIR difference spectra. This method is non-invasively and can be performed in real time which is a great advantage over other established methods as the determination of gel fractions [157], weight ratios [158], swelling properties [159] or rheology [160,161].…”

“…According to DFT calculations the cis -cycloadduct (see Figure 9c for the structure) cannot be distinguished easily by infrared spectroscopy from the trans- cycloadduct, since there are no prominent marker bands. However, due to its drilled ring system, an additional carbonyl vibration shows significant IR activity and thus contributes to the absorption spectrum [156]. …”

POSS Polyimide Sealed Flexible Triple‐Junction GaAs Thin‐Film Solar Cells for Space Applications

“…The original POSS polyimide (unexposed) shows vibration peaks matching with its chemical structure, with presence of benzene rings at 665–910 and 1435–1485 cm −1 , double bond CO at 1713–1780 cm −1 , and single bonds CO, CN, and CH at 1040–1050, 1125–1237, and 1320–1376 cm −1 . [ 40,41 ] FTIR peak positions keep stable after gammar ray exposure, electron exposure, and thermal cycling, indicating good durability of POSS polyimide upon these exposures. There are obvious changes in FTIR spectra after POSS polyimide films are exposed by AO, VUV, and electrons and protons.…”