The modified poly(p-phenylene benzobisoxazole) (PBO) containing polar hydroxyl groups in macromolecular chains was obtained by copolymerization from 1,3-diamino-4,6-dihydroxybenzene dihydrochloride (DAR) and terephthalic acid (TPA), with addition of certain amounts of 2,5-dihydroxyterephthalic acid (DHTA) in replace of TPA. The obtained DHPBO/PPA dope was directly spun into fibers via a dry-jet wet-spinning process. The resultant polymers were characterized mainly by means of FTIR, dynamic contact angle analysis, etc. FTIR spectrum of DHPBO fibers indicated that the hydroxyl groups were incorporated into the polymer chains. The contact angle results showed that the wetting process of ethanol on DHPBO was apparently faster than on PBO fibers. Single fiber pull-out test showed that DHPBO fibers had apparent larger IFSS value than PBO fibers. SEM proved that there was more resin remaining on the surface of DHPBO fibers than on PBO fibers after pull-out test, showing the improved surface adhesion ability of DHPBO. Meanwhile, axial compression bending and UV aging tests showed that the introduction of hydroxyl groups in the macromolecular chains apparently enhanced compressibility and resistance to ultraviolet radiation properties of DHPBO fibers.

Key words: hydroxyl group, dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) fiber, surface property, axial compression strength, resistance to ultraviolet radiation