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

12 February 2020, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

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(CH2)xCOCl (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 1H 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 1H 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.

Keywords

Poly(ester-imide)s
Copolymer sequences
Supramolecular chemistry
Fractals

Supplementary materials

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C7 Pyr heptamer-lowest energy
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c7 symmetric final pyr2 0 Start
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c7 symmetric final pyr2 2 First Minimum
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c7 symmetric final pyr2 7 Middle
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c7 symmetric final pyr2 11 Second Minimum
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c7 symmetric final pyr2 13 End
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Single-site ESI rev1
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Supplementary weblinks

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