The influence of phthalonitrile monomer containing oxazine ring on the properties of epoxy/amine system: Curing behavior and thermal stability

Phthalonitrile monomer containing oxazine ring (BPS-Ph) was synthesized using bisphenol-S, aniline, paraformaldehyde, and 4-nitrophthalonitrile via a two-step method. The differential scanning calorimetry (DSC) data of the curing process of BPS-Ph monomer indicates that the peak polymerization temperature of the cyan group is about 250°C and that confirms the promoting effect of oxazine ring on the curing reaction of phthalonitrile. The rheological data of E51/DDS containing BPS-Ph indicates that the BPS-Ph monomer also has promoting effect on the curing process. The activation energy was studied via the iso-conversional method principle. The activation energy corresponding to the E51/DDS crosslinking reaction is 75.79 and 60.54 kJ mol −1 , respectively, for pure E51/DDS and E51/DDS/BPS-Ph. Moreover, the activation energy of the crosslinking of phthalhydrazine is 74.1 kJ mol −1 which is rather lower than that in pure BPS-Ph, and that implies the synergistically catalytic effect of the oxazine ring and the amine. The addition of BPS-Ph monomer significantly improves the thermal behaviors of the thermoset. The char yield in N 2 atmosphere increased from 15.6% to 53.9% when adding 30% BPS-Ph to the E51/DDS. Moreover, the peak weight loss temperature decreased from 407 to 385°C. The phase separation size of poly-BPS-Ph in E51/DDS is about tens to hundreds nanometers according to the atomic force microscopy (AFM) phase diagram. It is indicated that incorporation of phthalonitrile monomer containing oxazine ring into epoxy/amine system is an applicable and effective way to promote the thermal behavior of the thermoset.