Catechol-based macrocyclic aromatic ether-sulfones: synthesis, characterization and ring-opening polymerization

Fabio Aricò,Howard M Colquhoun,Christopher A Ramsden

doi:10.24820/ark.5550190.p011.424

Abstract

Cyclocondensation between 4,4`-bis(4-chlorobenzenesulfonyl)biphenyl and catechol, with subsequent chromatographic separation of the reaction products, led to the isolation of four novel ether-sulfone macrocycles (cyclic dimer, -trimer, -tetramer and -pentamer). Similarly, cyclocondensation of catechol with a novel seven-ring diketone/disulfone monomer allowed the isolation of the two new aromatic ether-ketone-sulfone macrocycles, a cyclic monomer and a cyclic dimer. Transannular shielding and deshielding effects in the cyclic monomer produce substantial chemical shift differences for chemically equivalent protons in the 1H NMR spectra of the cyclic monomer and -dimer. Fluoride-initiated ring-opening polymerization of the ether-sulfone cyclic trimer affords a novel, high-molecular weight poly(ether-sulfone).

Highlights

The molecular structures of high-temperature engineering thermoplastics generally comprise linear chains of aromatic rings, linked together by thermo-oxidatively stable units such as direct arene-arene bonds, ether, ketone, sulfone, amide or imide groups.[1,2] Aromatic poly(ether-sulfone)s, exemplified in Chart 1, comprise an industrially-significant class of such polymers: these materials may in principle be accessed either by electrophilic chemistry[3] or by activated nucleophilic substitution[4] at the aromatic rings
We report the synthesis, characterization, and entropy-driven ring-opening polymerization of a novel series of macrocyclic aromatics derived from catechol by nucleophilic cyclo-condensation with extended aromatic dichloro-compounds, activated towards nucleophilic (SNAr) substitution by the presence of sulfone groups para to the chloro-substituents
Fractionation of the resulting mixture of cyclic oligomers by gradient elution chromatography afforded a series of macrocycles as pure compounds including the cyclo-dimer 2 (7.8%), -trimer 3 (3.4%), -tetramer 4 (2.0%) and -pentamer 5 (1.5%)

Summary

Introduction

The molecular structures of high-temperature engineering thermoplastics generally comprise linear chains of aromatic rings, linked together by thermo-oxidatively stable units such as direct arene-arene bonds, ether, ketone, sulfone, amide or imide groups.[1,2] Aromatic poly(ether-sulfone)s, exemplified in Chart 1, comprise an industrially-significant class of such polymers: these materials may in principle be accessed either by electrophilic chemistry (polysulfonylation)[3] or by activated nucleophilic substitution (polyetherification)[4] at the aromatic rings. In practice the nucleophilic route, involving the displacement of sulfone-activated chloride by phenoxide ion, has generally proved more selective and versatile both in the laboratory and in commercial production.[5,6] A more recently-discovered approach to polymers of this type involves the ring-opening polymerization (ROP) of macrocyclic aromatic (ether-sulfone)s.7,8 Macrocyclic oligomers are present in small, equilibrium quantities (typically 1–3 wt%) in many linear step-growth polymers, including the poly(ethersulfone)s,9,10,11 but they may be obtained in high yield either by cyclo-condensation of monomers under pseudo-high-dilution conditions,[12,13,14,15,16] or by ring-closing depolymerization of high molecular weight (MW) polymer at low concentration in solution.[7,17,18]

Results

Conclusion