Rheokinetic investigations on the thermal polymerization of benzoxazine monomer

The thermal cross-linking polymerization of bisphenol-A based benzoxazine was monitored at different isothermal curing temperatures by rheological analysis. An autocatalytic kinetic model was proposed for the curing of benzoxazine monomer. Gel point (t_gel) was determined from tan δ maximum and also from intercept of storage and loss modulus and the corresponding activation energy was estimated. All kinetic parameters including reaction orders and kinetic constants were determined. The autocatalytic effect was very significant. A master equation for the cure rate was generated from the kinetic data that was numerically integrated to predict the cure-profile. The theoretical cure prediction matched reasonably well with the experimental results. The high autocatalytic effect was attributed to the presence of phenolic OH groups generated by the ring-opening polymerization; which aids further ring-opening polymerization.