Effects of the Backbone’s Structures on the Curing Behaviors and Properties of Phthalonitrile Containing Benzoxazine Rings

Phthalonitrile-based resins and benzoxazine play important roles in the field of advanced materials because of their excellent properties. In order to understand the effect of the backbone's structure on the curing kinetics and properties of the multifunctional resin matrices, different kinds of phthalonitrile containing benzoxazine with various backbone structures were designed and prepared. The curing processes and curing behaviors were investigated by differential scanning calorimetry (DSC). With the assistance of the orthogonal test analysis method, the kinetic parameters, including activation energy <i>E_α</i>, were evaluated and calculated. Results indicated that an autocatalytic model for the curing reaction of various phthalonitrile-containing benzoxazine resins was confirmed. Nevertheless, the activation energies for reactions of benzoxazine and nitrile groups were significantly changed due to the steric hindrance derived from the backbone's structures. The thermal stability of polymers cured at various temperatures was evaluated by TGA testing. Then, their mechanical properties were investigated and confirmed with SEM images of fracture surfaces. Also, the thermal expansion characteristics of the various polymers were investigated. Results demonstrated that this work proposed an improved matrix resin system with outstanding thermal stability and mechanical properties that broadened the foundation and ideas for subsequent research.