Branched poly(ether sulfone)s were prepared from 1,1,1-tris(4-hydroxyphenyl) ethane and 4,4'-difluorodiphenyl sulfone (DFDPS) either by polycondensation in dimethyl sulfoxide with the elimination of water or via the silyl method in N-methylpyrrolidone. With an exact 1/1 stoichiometry, crosslinking was avoidable, but significant fractions of cyclic oligomers and polymers were detected by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Furthermore, bridged cycles (bicycles) were detected. For the silyl method, even an excess of DFDPS of 10 mol % did not result in crosslinking. The pendant OH groups were modified by acylation with acetic anhydride, methacrylic anhydride, undecylenoyl chloride, or cinnamoyl chloride. Alkylation was only successful in a one-pot procedure via the silyl method. Alkylbromide, ethyl bromoacetate, 3-chloropropionitrile, 4-nitrobenzyl bromide, and 3,4-dichlorobenzyl chloride served as alkylating agents. With 1,3-propane and 1,4-butane sultone, poly(ether sulfone)s with pendant sulfonate groups were obtained.