Understanding of the polymerization mechanism of the phthalonitrile-based resins containing benzoxazine and their thermal stability

As a unique class of high-performance phthalonitrile-based resins, phthalonitrile containing benzoxazine resin has attracted increasing interests in a widen application fields including aerospace, electronic packaging materials and flameresistant materials in marine. In order to reveal the polymerization mechanism of nitrile groups in the presence of benzoxazine, model experiments were designed and performed with three model compounds, which were synthesized according to the structures of the ring-opened benzoxazine rings. Model compounds with phenolic hydroxyl groups, amine structures and both of them were blended with bisphenol A phthalonitrile monomers and their curing behaviors were investigated by DSC and FTIR. Also, the possible polymerization process was proposed and discussed in detail. Results indicated that the polymerization of nitrile was promoted by the synergistic catalysis effects of the amine structures and the active hydrogen generated from the ring-opening of benzoxazine rings. The nitrile groups were firstly triggered by the lone pair electrons in amine structures and then the further polymerizations were promoted by the phenolic hydroxyl groups. Moreover, it was found that the compounds with well-ordered structures of phenol hydroxyl groups and amine structures exhibited relatively weak acceleration on the trigger polymerization of nitrile groups, while higher subsequent polymerization rate, in comparison with the other model compounds, which can be ascribed to their space configuration and the steric hindrance effects. Additionally, the thermal stability of the resulted polymers with various model compounds was studied to confirm the proposed polymerization mechanism and the final polymerization structures. (C) 2018 Elsevier Ltd. All rights reserved.