A series of novel semiaromatic (co) polyamides, poly(octylene terephthalamide)-ran-poly[octylene 2,5-bis(allyloxy)terephthalamide] (APA8T-x, x represents the molar fraction of allyloxy containing structure unit), were prepared via the interfacial polymerization of 1,8-diaminooctane, terephthaloyl chloride, and 2,5-bis(allyloxy) terephthaloyl chloride. The polymerization conditions were optimized in terms of the yields and the molecular weights of the resultant polymers. These polymers were converted to the target macromolecules, poly(octylene terephthalamide)- ran-poly[octylene (2,5-dihydroxy-3,6-diallyl)terephthalamide] (CRPA8T-x), through solid state Claisen rearrangement reaction, as characterized by H-1 NMR and FT-IR spectroscopies. While APA8T-x was only soluble in very limited solvents, the solubility of CRPA8T-x in polar solvents improved remarkably, especially for those with high counit content. Due to the polarity of hydroxyl group, CRPA8T-x showed an improved hydrophilicity than APA8T-x. The treatment of aramid fibers with CRPA8T-x, as sizing agents, enhanced obviously their interfacial adhesion toward epoxy resin. The fibers sized with 0.5 wt% CRPA8T-75 solution in the mixture of 1,1,2,2-tetrachloroethane and phenol (40: 60, w/w) exhibited a maximum increase of 60% in interfacial shear strength than the naked fibers. The easy preparation and the facility for the further modification through the dual functional substituents may greatly widen the application of semiaromatic polyamides. (C) 2016 Wiley Periodicals, Inc.