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

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 (H-1 and C-13) indicates that the monomer is only slightly activated or (F-19) 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 degreesC, and all the polymers have shown high thermooxidative stability, with 5% weight loss values in an air environment approaching 500 degreesC. (C) 2004 Wiley Periodicals, Inc.