Molecular dynamics simulations of thermomechanical properties of silicone-modified phenolic polymer

The silicone-phenolic multicomponent polymers are typically employed as the matrix of fiber-reinforced nanocomposites developed for reentry vehicles due to their excellent thermal and mechanical properties. The thermomechanical properties of the silicone-phenolic multicomponent polymer system, which are greatly related to the processing and microstructures, were studied using molecular dynamics (MD) simulations combined with experiments. A multistep dynamic polymerization approach was utilized to form the crosslinked polymer model, which was also validated in terms of both microstructures and properties. The thermomechanical properties of the crosslinked polymer system were established as a function of crosslinking degree, component ratio, temperature, strain rate, and cooling rate, and the influence mechanisms of the processing parameters were revealed. The crosslinking degree can greatly influence the glass transition temperature and volumetric coefficient of thermal expansion, which is attributed to the constrained chain mobility. The crosslinking degree and the component ratio have a significant effect on the morphologies and vibrational density of states of the polymer system, respectively, which in turn affects the thermal conductivity. The failure mode during uniaxial tensile was investigated in terms of the atomic energy distribution through MD simulations. The elastic and plastic deformation stages are dominated by intermolecular non-bonding interactions, but less contributed by the bonding interactions. This work can guide the design of polymeric nanocomposites by establishing the relationship of processing-microstructure-thermomechanical properties.