The polymerization behavior and thermal properties of benzoxazine based on o-allylphenol and 4,4′-diaminodiphenyl methane

Three bifunctional benzoxazines (oAP-ddm, oC-ddm, and P-ddm) were synthesized from 4,4′-diaminodiphenyl methane, formaldehyde, and three phenols, namely o-allylphenol, o-cresol, and phenol. The polymerization temperatures and activation energies of oAP-ddm and oC-ddm are very similar and higher than those of P-ddm; however, their reaction enthalpies exhibit inverse behavior. The storage moduli of the corresponding polybenzoxazines, PoAP-ddm, PoC-ddm, and PP-ddm, are approximately 2.1, 3.2, and 2.9 GPa at 25 °C, respectively, and their glass transition temperatures are 139, 166, and 198 °C, respectively. The thermal stabilities of PoAP-ddm and PoC-ddm are similar and lower than that of PP-ddm. The results indicate that polybenzoxazines based on ortho-substituted phenols provide higher flexibility than their counterparts prepared from unsubstituted phenol.