A novel polyarylene ether nitrile terminated with phthalonitrile (PEN-t-Ph) was synthesized by a simple solution polycondensation of biphenyl and hydroquinone with 2,6-dichlorobenzonitrile, followed by termination with 4-nitrophthalonitrile. The PEN-t-Ph/1,3,5-Tri-(3,4-dicyanophenoxy) benzene (TPh) system was prepared by cure treatment. The phthalonitrile on PEN-t-Ph were thermally crosslinked with TPh in the presence of diamino diphenyl sulfone through cure treatment up to 280-340 degrees C, which led to the transformation from thermoplastic polymers to thermosetting polymers. This is because the phthalonitrile on the PEN-t-Ph can react with TPh by forming phthalocyanine ring. The glass transition temperatures of the PEN-t-Ph/ TPh system increased from 152.4 degrees C to 194.7 degrees C, and the initial decomposition temperature (ranging from 475.3 degrees C to 544.0 degrees C) increased by 68 degrees C after thermal curing. Therefore, their thermal properties can be greatly enhanced by crosslinking. (C) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1363-1368, 2013