Theoretical Studies on the Thermal Stability of New Types of High Temperature Resistant Resins

The development of new resins with high heat resistance and excellent processing properties is of great significance to aerospace, communications, and electronics fields. In this work, density functional theory (DFT) is used to systematically study the bond dissociation energy (BDE) of main bonds in a series of new heat-resistant silane-arylacetylene resin, aromatic heterocyclic-containing resin, and cyano-containing resin molecules. The DFT-B3LYP functional and 6-31g(d,p) basis set are adopted to make all resin molecules relax fully. The vibrational analysis results show that all resin molecules have no imaginary frequency, indicating that they correspond to the stable configuration on their potential energy surfaces. Then, BDEs of the main chemical bonds in all resin molecules are calculated. This work mainly studies the thermal stability of resin monomer molecules, so the thermal stability of the monomer molecules can be measured by calculating BDE of the main bonds in the resin monomer molecules. In fact, the curing reaction of the resin monomer molecules at high temperature usually occurs on the branches, while the ring remains unchanged. The heterocyclic ring and benzene ring are aromatic, and BDEs of the bonds on the rings are higher than those of the non-cyclic bonds. Therefore, BDEs of the bonds on the rings in the resin monomer molecules are not considered in this work. At the same time, the reactants and free radical products are optimized and the vibrational analysis is performed. The results show that the cyano-containing resin molecules have higher thermal stability than the silane-aryne-containing resin molecules and aromatic heterocyclic-containing resin molecules, indicating that the introduction of cyano groups into the resin molecules is more helpful for improving their thermal stability than the introduction of silane-arylalkynyl and aromatic heterocycles groups. Our studies find the weakest bond in each resin molecule and reveal the essence of its thermal stability at the microscopic level, which provide a theoretical basis for the design, synthesis, and application of new high temperature resistant resins.