Two kinds of modified poly(p-phenylene benzoxazole) (PBO), the copolymer of TPA (SPBO) and p-SPBO, containing ionic groups in the macromolecular chains were obtained by copolymerization from 1,3-diamino-4,6-dihydroxybenzene dihydrochloride (DAR) and terephthalic acid (TPA), with the addition of selected amounts (1.5-5.0% molar ratio over DAR) of 5-sulfoisophthalic acid monosodium salt or sulfolerephthalic acid monopotassium salt in place of the TPA, respectively, in poly(phosphoric acid) (PPA). The resultant PBO/PPA, SPBO/PPA, and p-SPBO/PPA lyotropic liquid-crystalline solutions were spun into fibers by a dry-jet wet-spinning technique. Chemically modified PBO fibers with sulfonate salt pendants in the polymer chains were obtained for the first time. The surface wetting behavior and interfacial shear strength between the fiber and epoxy resin were investigated. The interference of sulfonate salt pendants on the crystalline morphology was measured. (C) 2008 Wiley Periodicals, Inc.