A polyfunctional arylacetylenic monomer, 1,2,4-tris(phenylethynyl)benzene, thermally polymerizes by a free-radical mechanism to a highly crosslinked structure of interest as a precursor matrix for carbon/carbon composites. The polymerization reaction was characterized by Fourier transform infra-red spectroscopy and differential scanning calorimetry (d.s.c.). The disappearance of the acetylenic stretching band at 2212 cm-1 was used successfully to monitor the cure reaction. The cure reaction follows first-order kinetics with an overall activation energy of 135 kJ mol-1. Dynamic d.s.c. analysis carried out to estimate the activation energy of the cure reaction yields a value of 137 kJ mol-1.