Thermal curing mechanism of acetylene-terminated polyimides: A combination of density functional theory computation and microkinetic analysis
Thermal curing mechanism of acetylene-terminated polyimides: A combination of density functional theory computation and microkinetic analysis
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端乙炔聚酰亚胺的热固化机理：密度泛函理论计算与微动力学分析的结合
DOI：
10.1016/j.polymer.2021.123529
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发表时间：
2021-02-20
期刊：
影响因子：
4.6
通讯作者：
Du, Lei
中科院分区：
文献类型：
--
作者：
Chen, Zuowei;Wang, Liquan;Du, Lei
乙炔封端聚酰亚胺的力学和热性能高度依赖于交联结构。然而，由芳基乙炔基形成的交联仍然是难以捉摸的，这导致在调整最终树脂的性能方面的困难。因此，从根本上了解端乙炔基聚酰亚胺的固化机理，预测其固化产物，对开发新型耐高温树脂具有重要意义。本文对乙炔封端聚酰亚胺的热固化反应进行了量子化学计算和微观动力学分析。提出了萘二聚体、苯三聚体和单自由基的初始生成途径，并研究了单自由基引发乙炔基自由基聚合的反应。最后，从头算为基础的微观动力学分析进行了使用动力学蒙特卡罗模拟。计算结果表明，较高的固化温度和较低的芳基乙炔基的初始浓度导致较高的苯三聚体的百分比和减少的多烯链，和萘二聚体中存在的一小部分。环丁烯基和环己二烯基自由基分别由反式和顺式增长链的分子内环化形成，在确定固化产物的组成中起着至关重要的作用。固化条件对交联度影响的研究结果与已有的实验结果吻合较好。该工作也可为调整最终固化树脂的结构提供指导。
The mechanical and thermal properties of acetylene-terminated polyimides are highly dependent on the cross-linked structures. However, the cross-links formed from arylethynyl groups are still elusive, which causes dif-ficulty in tuning the performance of final resins. Therefore, fundamentally understanding the curing mechanisms and predicting the cured products of acetylene-terminated polyimides are of great importance for developing new high-temperature resins. We present quantum chemical computations together with microkinetic analysis on the thermal curing reaction of acetylene-terminated polyimides. The initial pathways of forming the naph-thalenic dimer, benzenic trimer, and monoradicals were put forward, and then the radical polymerization of ethynyl groups initiated by monoradicals was investigated. Finally, an ab initio based microkinetic analysis was performed by using a kinetic Monte Carlo simulation. The computational results indicated that a higher curing temperature and lower initial concentration of arylethynyl groups result in a higher percentage of benzenic trimer and a decrease of polyenic chains, and the naphthalenic dimer is present in a minor fraction. The cyclobutenyl and cyclohexadienyl radicals formed by intramolecular cyclization of trans and cis growing chains, respectively, play an essential role in determining the composition of cured products. The results about the effect of curing conditions on cross-links are in good agreement with the existing experimental results. The work can also provide guidance for tuning the structure of final cured resins.