Study of the curing kinetics of a benzimidazole/phthalonitrile resin system

The isothermal curing behaviour of a benzimidazole/phthalonitrile (PNBI/PNTI) resin system was studied by rheology, quasi-isothermal modulated differential scanning calorimetry (QMDSC) and polarised optical microscopy (POM) in combination with theoretical model analysis. The rheological curing kinetics are consistent with an apparent self-acceleration model d alpha/dt = k alpha(m)(1 - alpha)(n) below conversion a = 80% with a total reaction order m + n of approximately 2.3. Viscosity analysis and POM show that microphase separation has already occurred in the initial cure stages, which is responsible for the extremely mild curing process and apparent self-acceleration model. Changes in the effective activation energy of the curing system with conversion alpha were introduced to include the effects of diffusion control. A new equation for diffusion factor (DF) based on the law of addition of kinetic resistance and the equation of effective activation energy has been induced, indicating that the values of DF are primarily determined by the effective activation energy. (C) 2014 Published by Elsevier B.V.