Chen Zuowei, Wang Liquan, Lin Jiaping, Du Lei
Shanghai Key Laboratory of Advanced Polymeric Materials, Key Laboratory for Ultrafine Materials of Ministry of Education, Frontiers Science Center for Materiobiology and Dynamic Chemistry, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China.
Phys Chem Chem Phys. 2021 Aug 28;23(32):17300-17309. doi: 10.1039/d1cp01947c. Epub 2021 Aug 3.
High-temperature phthalonitrile resins have a wide range of applications, and understanding their curing mechanism is of great importance for academic research and engineering applications. However, the actual curing mechanism is still elusive. We presented a density functional theory study on the curing mechanism of phthalonitrile resins promoted by aromatic amines using phthalonitrile and aniline as the model compounds. We found that the rate-determining step is the initial nucleophilic addition of amines with nitrile groups on phthalonitrile to generate an amidine intermediate. The amines play a vital role in the H-transfer promoter throughout the curing reaction. The amidine and isoindoline are the critical intermediates, which can readily react with phthalonitrile through 6-membered transition states. The intramolecular cyclization of amidine intermediates is the vital step in forming isoindoline intermediates, which can be significantly promoted by amines. The proposed curing reaction pathways are kinetically more favorable than the previously reported ones, which can account for the formation of triazine, polyisoindoline, and phthalocyanine and provide a molecular-level understanding of the curing reaction.
高温邻苯二甲腈树脂有广泛的应用，了解它们的固化机理对学术研究和工程应用非常重要。然而，实际的固化机理仍然难以捉摸。我们以邻苯二甲腈和苯胺为模型化合物，对芳香胺促进邻苯二甲腈树脂固化机理进行了密度泛函理论研究。我们发现，速率决定步骤是胺与邻苯二甲腈上的腈基进行初始亲核加成以生成脒中间体。在整个固化反应中，胺在氢转移促进剂中起着至关重要的作用。脒和异吲哚啉是关键中间体，它们可以通过六元过渡态与邻苯二甲腈轻松反应。脒中间体的分子内环化是形成异吲哚啉中间体的关键步骤，胺可以显著促进这一步骤。所提出的固化反应途径在动力学上比先前报道的途径更有利，这可以解释三嗪、聚异吲哚啉和酞菁的形成，并提供对固化反应的分子水平理解。
