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An m. p. of 106-107" has been given 2O for the acid.

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High-temperature (330 °C) polycondensation of 4,4'-dihydroxydiphenyl sulfone with 4,4'bis(4-fluorobenzoyl)biphenyl, using diphenyl sulphone as solvent and sodium carbonate as base, leads to formation of an amorphous polymer (A) in which the monomer-derived subunits [-OArSOjAr-] ("S") and [OArCOArArCOAr-] ("K") essentially alternate along the polymer chain. In contrast, the polymer (B) formed on replacing part (ca. 10%) of the sodium carbonate by potassium carbonate is partially crystalline, and sequence analysis by 13C NMR indicates that the distribution of S and K units within a chain is now almost entirely random. The crystalline phase of polymer B is identified as [-OArCOArArCOAr-]", and a structure is proposed for this phase on the basis of X-ray fiber studies, single-crystal X-ray oligomer data, and molecular-modeling/diffraction-simulation techniques.