Single-Site Binding of Pyrene to Poly(ester-Imide)s Incorporating Long Spacer Units: Prediction of NMR Resonance-Patterns from a Fractal Model

Authors:
  • MKMarcus Knappert
    Marcus Knappert
  • TJTianqi Jin
    Tianqi Jin
  • SMScott D. Midgley
    Scott D. Midgley
  • GWGuanglu Wu
    Guanglu Wu
  • OSOren Scherman
    Oren Scherman
  • RGRicardo Grau-Crespo
    Ricardo Grau-Crespo
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Abstract
Co-polycondensation of the diimide-based diols N , N '-bis(2-hydroxyethyl)hexafluoro-isopropylidene-diphthalimide, (HFDI), and N , N '-bis(2-hydroxy-ethyl)naphthalene-1,4,5,8-tetracarboxylic-diimide, (NDI), with aliphatic diacyl chlorides ClOC(CH 2 ) x COCl ( x = 5 to 8) affords linear copoly(ester-imide)s. Such copolymers interact with pyrene via supramolecular binding of the polycyclic aromatic molecule at NDI residues. This results in upfield complexation shifts and sequence-related splittings of the NDI 1 H NMR resonances, but gives a very different resonance-pattern from the corresponding copolymer where x = 2. Computational modelling of the polymer with x = 5 suggests that, in this system, each pyrene molecule binds to just a single NDI residue rather than to an adjacent pair of NDI's in a tight chain-fold ("dual-site" binding) as found for x = 2. The new single-site binding model enables the pattern of 1 H NMR resonances for copolymers with longer spacers ( x = 5 to 8) to be reproduced and assigned by simulation from sequence-specific shielding factors based on the fractal known as the fourth-quarter Cantor set. As this set also enables an understanding of dual-site binding systems, it evidently provides a general numerical framework for supramolecular sequence-analysis in binary copolymers.
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