Thianthrene as an activating group for the synthesis of poly(aryl ether thianthrene)s by nucleophilic aromatic substitution

Abstract

A method for the preparation of poly(aryl ether thianthrene)s has been developed in which the aryl ether linkage is generated in the polymer‐forming reaction. The thianthrene heterocycle is sufficiently electron‐withdrawing to allow fluoro displacement with phenoxides by nucleophilic aromatic substitution. The monomer for this reaction, 2,7‐difluorothianthrene, can be synthesized in a moderate yield by a simple reaction sequence. Semiempirical calculations at the PM3 level suggest that 2,7‐difluorothianthrene is sufficiently activated, whereas NMR spectroscopy (1H and 13C) indicates that the monomer is only slightly activated or (19F) not sufficiently activated for nucleophilic aromatic substitution. Model reactions with p‐cresol have demonstrated that the fluorine atoms on 2,7‐difluorothianthrene are readily displaced by phenoxides in high yields, and the process has been deemed suitable for polymer‐forming reactions. High‐molecular‐weight polymers have been produced from bisphenol A, bisphenol AF, and 4,4′‐biphenol. The polymers have been characterized with gel permeation chromatography, NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. The glass‐transition temperatures for the polymers of different compositions and molecular weights range from 138 to 181 °C, and all the polymers have shown high thermooxidative stability, with 5% weight loss values in an air environment approaching 500 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6353–6363, 2004

Poly(aryl ether sulfide)s by sulfide-activated nucleophilic aromatic substitution polymerization

“…This monomer is a high melting crystalline solid that sublimes under reduced pressure, compared to the liquid bis(4-fluorophenyl)sulfide, simplifying purification for polymer synthesis. We have recently demonstrated the reactivity of 2,7-difluorothianthrene as an activated monomer for nucleophilic aromatic substitution and have produced high molecular weight poly(aryl ether thianthrenes) under fairly mild reaction conditions [51]. The high molecular weight further demonstrates the general activation by a sulfide group for nucleophilic aromatic substitution.…”

“…We are interested in investigating other activating groups that may not be obvious choices as strongly electron withdrawing groups, and may not follow the traditional ideas of Meisenheimer complex activation [50,51]. We have found different types of activating groups para to a fluoro group to undergo essentially quantitative nucleophilic aromatic substitution with phenoxides by what appears to be a S N Ar mechanism.…”

“…Continued research will help to elucidate a mechanism, but will focus ultimately on the formation of new materials and their characterization and use. We have investigated two different activation ideas-electron accepting heteroatom activation [51] and ring-opening Meisenheimer stabilization [50].…”

“…Toluene (HPLC grade) was washed with cold concentrated sulfuric acid, three times with water, dried over calcium chloride, and then distilled from sodium metal under Polymer 47 (2006) The synthesis of 2,7-difluorothianthrene and its polymerization with bisphenol A, bisphenol AF, and biphenol to make poly(aryl ether thianthrene)s has been recently described [51].…”

“…Mohanty has studied the activation of aryl fluorides by diazo groups, the synthesis of block copolymers of poly(aryl ether)s, and competitive radical reactions [42][43][44][45][46][47][48]. We have also been active in this area through the investigation of azomethines as activating groups [49] and through continuing recent research on the activation of aryl fluorides for nucleophilic aromatic substitution by using groups that are not strong electron withdrawing groups, but which can activate the substitution by electron accepting means [50,51]. This paper will describe some of the recent results obtained in our group on the activation of aryl fluorides for substitution by nucleophilic aromatic substitution polymerization and the material properties of the polymers.…”