A new thermally reactive monomer has been designed and synthesized that brings novel crosslinking chemistry to high-performance polymers. This monomer (XTA) is a derivative of terephthalic acid and was based on the thermal chemistry of benzocyclobutene. Various model compounds have been synthesized to investigate substituent effects on benzocyclobutene reactivity. Irreversible reaction exotherms around 350 degrees C were observed in these model compounds using differential scanning calorimetry. Based on these studies, polyaramid and poly(aryl ether ketone) XTA copolymers were synthesized. The formation of an insoluble network resulted after heat treatment of these polymers.