(563e) Investigation of Epoxy Network Formation by Simulation and Experiment

Diglycidyl ether of bisphenol-A (DGEBA) and diethylenetriamine (DETA) react to form a highly cross-linked epoxy network. We investigated the cure kinetics of this epoxy system as a function of its chemical composition using a combination of inelastic light scattering and molecular dynamics (MD) simulations. Using concurrent Brillouin and Raman scattering we monitored both the changes in visco-elastic properties and chemical signatures of the epoxy in situ, while it was polymerizing. The complex mechanical modulus revealed by Brillouin scattering provides the most direct measure of the structural integrity of the polymer network. In order to establish the relationship between degree of cure and the elastic modulus of the resulting structure, we carried out multi-scale molecular simulations. We generated epoxy networks using a combination of MD and a heuristic bond exchange protocol. Mechanical properties of these networks were evaluated, by subjecting them to tensile and shear tests at various degrees of reaction. Raman active vibrational modes for the various structural moieties were predicted using density functional theory calculations and weighted according to their concentrations in MD-simulated structures to generate Raman spectra as a function of the degree of cure. Finally, all experimental and simulation data were combined in a system of differential equations to establish a model for the epoxy cure kinetics in way consistent with all methods of investigation.