Macrocycles. 18. The Role of Cyclization in Syntheses of Poly(ether−sulfone)s

Poly(ether−sulfone)s having an identical backbone were prepared by four different methods. First, silylated bisphenol A (BSBA) was polycondensed with 4,4‘-difluorodiphenyl sulfone (DFDPS) and K 2 CO 3 in N -methylpyrrolidone with variation of the temperature. Second, analogous polycondensation were conducted using CsF as catalyst (and no K 2 CO 3 ). Third, CsF-catalyzed polycondensations BSBA and DFDPS were conducted in bulk up to 290 °C. Fourth, free bisphenol was polycondensed with DFDPS or 4,4‘-dichlorodiphenyl sulfone and K 2 CO 3 in DMSO with azeotropic removal of water. MALDI−TOF mass spectroscopy revealed that the first method mainly yielded cyclic poly(ether−sulfone)s which were detected up to masses around 13 000 Da. These and other results suggest that these polycondensations take a kinetically kontrolled course at tempeatures ≤145 °C. This interpretation is also valid for the fourth method where high yields of cycles were obtained with DFDPS. With the less reactive 4,4‘-dichlorodiphenyl sulfone lower conversions, lower molecular weights and lower fractions of cycles were found. In contrast to KF (resulting from K 2 CO 3 ) CsF cleaves the poly(ether sulfone) backbone at temperatures > 145 °C. Smaller amounts of smaller cycles were found in these CsF-catalyzed polycondensations which were in this case the result of thermodynamically controlled “back-biting degradation”.