title: 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.
authors.affiliation: Institute of Physical Chemistry, Heinrich-Heine University, Düsseldorf, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Hunger
authors.forename: Laura
authors.initials: L
authors.lastname: Buschhaus
authors.forename: Nadine
authors.initials: N
authors.lastname: Schmeling
authors.forename: Claudia
authors.initials: C
authors.lastname: Staudt
authors.forename: Anna
authors.initials: A
authors.lastname: Pfeifer
authors.forename: Karl
authors.initials: K
authors.lastname: Kleinermanns
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry*; D019281:Dimerization; D008301:Maleimides / Q000737:chemistry*; D008567:Membranes, Artificial; D015394:Molecular Structure; D055668:Photochemical Processes; D011789:Quantum Theory; D012117:Resins, Synthetic / Q000737:chemistry*
chemical_list: D003432:Cross-Linking Reagents; D008301:Maleimides; D008567:Membranes, Artificial; D012117:Resins, Synthetic; C043592:maleimide; C029945:polyimide resin