Using differential scanning calorimetry, we have investigated three difunctional cyanate monomers differing by their central group : bisphenol A dicyanate (BADCy), bisphenol E dicyanate (BEDCy), and hexafluorinated bisphenol A dicyanate (BAFDCy), to determine the effect of the central group on the molten state reactivity of heat-treated cyanates. To identify the different phenomena occurring during the heat cycle, which was followed by differential scanning calorimetry, C-13-NMR (Liquid and solid) was undertaken. This technique was used to characterize the major products and side products formed. Using C-13-NMR and HPLC, we were able to detect the formation of compounds with a triazine ring at one chain end and a hydroxyl function at the other. The presence of the latter depended on the purity of the initial monomers. In light of the purity parameter, inherent in the synthesis of the products, we propose an order of reactivity, at molten state, of the polymerization of the three cyanate monomers in the temperature range of 180-300 degrees C.