| Abstract
| - Polyphenylquinoxalines (PPQs) are prepared from self-polymerizable quinoxaline monomers that carry fluorine,hydroxyaryl (ArOH), and phenyl substituents. In basicmedia, these monomers self-polymerize via a series ofnucleophilic aromatic substitution reactions (SNAr), inwhich aromatic enolates (ArO- nucleophiles) attack theelectrophilic carbons bearing F leaving groups to effectfluoride displacement. Polyphenylquinoxaline/polyethersulfone (PPQ/PES) copolymers are synthesized similarlyby combining self-polymerizable quinoxaline monomerswith a 1:1 molar mixture of 4,4‘-dichlorodiphenyl sulfoneand bisphenol A. The MALDI mass spectra of the polymers reveal that the major products up to ∼15 000 Damolecular mass are homo- or copolymeric macrocycles.Linear byproducts are also observed, arising from nucleophilic ring opening of already formed macrocycles.Oligomers containing at least one PPQ unit readily protonate upon MALDI, whereas PES homopolymers requirealkali metal ion addition to become detectable. Molecularorbital calculations point out that the nucleophilic andelectrophilic reactivities of the PPQ monomer and thePPQ growing chains generated during propagation arecomparable, allowing for continued condensations via SNAr, until cyclization terminates this process. The calculations also predict a significantly lower electrophilic reactivity for carbons substituted by chlorine instead offluorine, justifying the discrimination against incorporation of PES units observed for the copolymers. Thecomputationally optimized structures of PPQ and PPQ/PES macrocycles show a diverse array of cavity sizes andgeometries which depend on the size of the macrocycle,the sequence of the repeat units, and the position of thesubstituents in the quinoxaline ring; quinoxaline pendants(phenyl groups) are found to favor helical arrangementsin the prepared macrocycles.
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