Molecular dynamics simulations on miscibility, glass transition temperature and mechanical properties of PMMA/DBP binary system

Polymethyl methacrylate (PMMA) and dibutyl phthalate (DBP) binary system was simulated by molecular dynamics (MD) simulations with the COMPASS force field to predict properties of PMMA/DBP blends such as the miscibility, the glass transition temperature (T_g) and mechanical properties of polymer/plasticizer blends. Results show that PMMA/DBP is a miscible system, which can be predicted by comparing the difference of the solubility parameters value (|Δδ|<2.0 MPa^0.5) between PMMA and DBP. The free volumes (V_F) and density (ρ) of PMMA/DBP system were simulated to study the T_g. It is found that the V_F and ρ of PMMA/DBP change regularly along with the increase of DBP mass fraction and the transition occurred at the turning point. We also predicted the effects of temperature and DBP on the mechanical properties of PMMA including Young's modulus (E), Bulk modulus (K), Shear modulus (G) and Poisson's ratio (v). The mechanical properties can be effectively improved by the temperature and the addition of DBP plasticizer, which may provide a more flexible mixture with a lower E, K, G and an increased ductility. Accordingly, the method used in this work is not only a useful tool to provide properties of a given polymer/plasticizer blend but also a promising technique to help screen the formulations of polymer bonded explosive (PBX) and propellants before experiments.