Characterization methods to inform reactive molecular dynamics simulations of the BMI resin curing process*

Bismaleimide (BMI) resins are an increasingly common polymer matrix material for fiber reinforced composites in aerospace applications. BMIs are especially well-suited to aerospace applications due to their relatively low density, minimal cure shrinkage, and limited moisture absorption. BMIs also have excellent thermo-mechanical and oxidative stability. Despite years of study, the complex combination of reactions that occur during the BMI polymerization and cross-linking process (cure) remain poorly understood. Our limited understanding of the resulting BMI network structure presents a barrier to physics-informed cure process optimization and multiscale modeling of composite materials. In this work, we investigate a variety of experimental characterization methods that can complement reactive molecular dynamics (MD) simulation and help build a clearer picture of the BMI cure process. MD simulations are carried out in LAMMPS using the interface force field (IFF) and REACTER package. Measured resin density and glass transition temperature values show reasonable agreement with simulation. DMA, dilatometry, and gel fraction measurements are collected to further investigate the correlations between the as-cured resin network and the MD simulation. Experimental findings are used to adjust simulation parameters, thereby increasing the utility of the model.