Curing Reaction of Benzoxazine Under High Pressure and the Effect on Thermal Resistance of Polybenzoxazine

Two benzoxazine monomers, bisphenol A/aniline type benzoxazine (BA-a) and bisphenol A/tert-butylamine type benzoxazine (BA-tb), are prepared with high purity. Their curing behaviors and cure kinetics are studied by high pressure differential scanning calorimetry (HP DSC) at normal pressure and high pressure, respectively. Meanwhile, the apparent activation energy (E-a) is calculated by Kissinger and Ozawa methods. The results show that the curing reaction temperature and E-a of BA-a are little influenced by high pressure, but for BA-tb, its curing reaction temperature and E-a increase greatly. FTIR is used to analyze the difference in the hydrogen bonds in cross-linking structures of cured BA-a and BA-tb. Also, molecular simulations are used to figure out the effect of the high pressure on chemical structures. It is found that the content of hydrogen bonds in polybenzoxazines cured at high pressure increases, resulting in the decrease of cross-linking densities. Moreover, DSC and thermogravimetric analysis tests are carried out to study the thermal resistance of these polybenzoxazines, and the results indicate that their glass transition temperatures (T(g)s) and thermal stability decrease after curing at high pressure.