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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.