Effects of chain length of nonaromatic epoxy resins on thermomechanical and optical properties: Experiment, ab initio, and molecular dynamics simulations

Epoxy resin has been extensively used in the field of advanced electronic materials as an adhesive and encapsulant owing to its excellent material properties. However, recently, there has been a demand for further improvement in heat resistance, high transparency, environmental resistance, and enhanced handling properties for high-brightness light-emitting diodes. Conventional aromatic epoxy resins lack light resistance; therefore, a colorless and transparent epoxy resin without aromatic rings is desirable. In this study, tris(2,3-epoxypropyl) isocyanurate (TEPIC) was used as a nonaromatic epoxy resin, and three types of TEPIC with different side-chain lengths were prepared. The ultraviolet (UV)-visible absorption properties of TEPIC were evaluated using time-dependent density functional theory, and the practicality of the numerical prediction of light resistance was verified. TEPIC yields a UV absorbance spectrum with a lower intensity than those of conventional aromatic epoxy resins, suggesting that TEPIC is expected to have high light resistance. In addition, their thermomechanical properties and the influence of molecular structure were evaluated using both molecular dynamics (MD) simulations and experiments. The MD simulation and experimental results were in good agreement, indicating that the long side chains of TEPIC suppress triaxial deformation-induced failure and improve ductility instead of decreasing strength and stiffness. In addition, the longer side chains form a dense molecular structure with less free volume. These results indicate that numerical approaches can be used to predict various properties of epoxy resins and interpret them from the molecular structure. Accordingly, these approaches can be used to aid the material development process.