%!3484& Two classes of poly(ether ketone)s were prepared from bisphenol-A, namely by polycondensation with 11 1 1 -difluorobenzophenone or with 2,6-difluorobenzophenone and 1 1 -tert.butyl-2,6-difluorobenzophenone. Two different synthetic methods were compared. First, polycondensations of the free bisphenol-A in DMSO or sulfolane with azeotropic distillation of water. Second, polycondensations of bistrimethylsilyl bisphenol-A in 2-methylpyrrolidone. The second approach gave higher yields and higher molecular weights (31 values up to 85000 Da and 32 values up to 190000 Da). The matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra revealed that the fraction of cyclic oligomers and polymers systematically increased with higher molecular weights. A few polycondensations of silylated 4-tert.butylcatechol with 11 1 1 -difluorobenzophenone confirmed the trends observed for silylated bisphenol-A. Under optimum conditions cyclic poly(ether ketone)s were detectable in the MALDI-TOF mass spectra up to molecular weights of 18 000 Da.'$ (83& Polycondensation, poly(ether ketone)s, cyclic polymers, bisphenol-A, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) !"#!Quite recently we have demonstrated [1-4] that the classical theory of step-growth polymerizations as it was elaborated by Carothers [5] and Flory [6, 7] is partially misleading because it ignores the role of cyclization reactions. In agreement with the calculations of Stepto and coworkers [8] or Gordon and coworkers [9] it was found that in kinetically controlled polycondensations (no equilibration reactions) cyclization competes with chain growth at any concentration (also in bulk) and at any stage of the polycondensation. Therefore, a clean polycondensation conducted up to 100% conversion should yield 100% cyclic reaction products.