The solid state cross-linking reactions occurring after the thermal priming of different bismaleimide monomers with variable steric hindrance were examined. As a result of the insolubility of the materials, monitoring reaction mixtures over time requires the use of techniques adapted to characterizing solids. After defining system reactivities by differential scanning calorimetry, most of the results could be obtained from spectral data furnished by FTi.r. and solid-state carbon-13 CP-MAS n.m.r.