Kinetics of Alder-ene reaction of Tris(2-allylphenoxy)triphenoxycyclotriphosphazene and bismaleimides — a DSC study

Tris(2-allylphenoxy)triphenoxycyclotriphosphazene was reacted with three bismaleimides (BMI), viz. bis(4-maleimido phenyl)methane (BMM), bis(4-maleimido phenyl)ether (BME) and bis(4-maleimido phenyl)sulphone (BMS) via the Alder-ene reaction. The differential scanning calorimetric analysis of the blend manifested two distinct exotherms. The low temperature exothermic reaction was attributed to the Wagner-Jauregg reaction following the ene reaction and the strong exotherms at around 250–270°C to the cross-linking Diels–Alder reactions of the initially formed adducts. The Kinetic parameters, viz. activation energy (E) and pre-exponential factor (A) of the reactions were evaluated by Kissinger and Ozawa methods using the variable heating rate method. The kinetic data revealed that the Wagner-Jauregg reaction was disfavoured by electron-withdrawing nature of the BMI. The Diels–Alder reaction was facilitated by the electron-withdrawing nature of the bismaleimide. The activation energy for the first exothermic stage decreased and for the second major step increased on enhancing the stoichiometry of BMI in the blend for a given pair. The activation parameters served to predict the isothermal cure profiles of the blends and deduce the possible network structure under the given conditions of cure temperature and stoichiometry.