Mechanistic and kinetic insights into phenol-catalyzed cyclotrimerization of cyanate esters

Abstract

Differential scanning and combustion calorimetry in combination with isoconversional methodology and chromatography are applied to acquire kinetic and mechanistic insights into the reaction of phenol-catalyzed cyclotrimerization of cyanate ester. The only detectable reaction intermediate is found to be imidocarbonate, which is demonstrated to form in an irreversible manner. Isoconversional analysis indicates that the overall reaction kinetics at its early and late stages is respectively controlled by the irreversible formation of imidocarbonate (Ea≈40 kJ mol−1) and a reaction of imidocarbonate with cyanate ester (Ea≈70 kJ mol−1). Cyclotrimerization of neat imidocarbonate is analyzed as well. For this reaction, no intermediates are detected. Its overall kinetics is determined to occur as a single autocatalytic step. It is concluded that cyclotrimerization of imidocarbonate does not amount to any significant competition to the reaction between imidocarbonate and cyanate ester.