Pham My-Phuong, Pham Buu Q, Huynh Lam K, Pham Ha Q, Marks Maurice J, Truong Thanh N
Institute for Computational Science and Technology, Ho-Chi-Minh City, Vietnam.
J Comput Chem. 2014 Aug 15;35(22):1630-40. doi: 10.1002/jcc.23658. Epub 2014 Jun 16.
A comprehensive picture on the mechanism of the epoxy-phenol curing reactions is presented using the density functional theory B3LYP/ 6-31G(d,p) and simplified physical molecular models to examine all possible reaction pathways. Phenol can act as its own promoter by using an addition phenol molecule to stabilize the transition states, and thus lower the rate-limiting barriers by 27.0-48.9 kJ/mol. In the uncatalyzed reaction, an epoxy ring is opened by a phenol with an apparent barrier of about 129.6 kJ/mol. In catalyzed reaction, catalysts facilitate the epoxy ring opening prior to curing that lowers the apparent barriers by 48.9-50.6 kJ/mol. However, this can be competed in highly basic catalysts such as amine-based catalysts, where catalysts are trapped in forms of hydrogen-bonded complex with phenol. Our theoretical results predict the activation energy in the range of 79.0-80.7 kJ/mol in phosphine-based catalyzed reactions, which agrees well with the reported experimental range of 54-86 kJ/mol.
利用密度泛函理论B3LYP/6 - 31G(d,p)和简化的物理分子模型研究所有可能的反应途径，给出了环氧-苯酚固化反应机理的全貌。苯酚可以通过添加一个苯酚分子来稳定过渡态，从而充当自身的促进剂，进而将限速势垒降低27.0 - 48.9 kJ/mol。在无催化反应中，苯酚使环氧环开环，表观势垒约为129.6 kJ/mol。在催化反应中，催化剂在固化前促进环氧环开环，使表观势垒降低48.9 - 50.6 kJ/mol。然而，在强碱性催化剂（如胺基催化剂）中会存在竞争，在这种情况下，催化剂会以与苯酚形成氢键络合物的形式被捕获。我们的理论结果预测，在膦基催化反应中活化能在79.0 - 80.7 kJ/mol范围内，这与报道的54 - 86 kJ/mol的实验范围吻合良好。
