The formation and scission of chemical bonds is encountered in a wide spectrum of materials. Theoretical modeling of these processes is challenging due to the large number of degrees of dynamical and non-dynamical correlation involved. Towards this goal, we investigate covalent bond breaking in polymers under high strain. Employing a hybrid method recently developed in-house, a mechanical strain is applied to the system in a classical mechanics simulation; when a bond is stretched past a threshold value, a region determined on-the-fly is subjected to a quantum mechanics (QM) optimization to determine which bonds break. The classical simulation is then resumed at progressively larger strains until another QM calculation is triggered. Our simulations show that for the system containing DGEBA cross-linked with MDA, there is a persistent pattern of the types of bonds most frequently broken under strain: The bonds between the benzylic carbon and the phenyl group in DGEBA were the most frequently broken, even when other types of bonds (C-N and C-O) triggered the QM calculation. Using natural bond orbitals (NBO) analysis, we demonstrate that the observed bond breaking patterns are direct results of hyperconjugative interactions in this system. This study offers the possibility to systematically and accurately predict the ultimate strength of composite materials.

Bond breaking in epoxy systems

2019 Spring National Meeting

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