Developing a Transferable Coarse-Grained Model for the Prediction of Thermodynamic, Structural and Mechanical Properties of Polyimides at Different Thermodynamic State Points.

In the present work, we develop a coarse-grained (CG) model for polyimide (PI) at 800 K and 1 atm by applying iterative Boltzmann inversion (IBI) and the density correction method to derive the bonded and nonbonded interaction potentials. Although the CG force field is built at a single thermodynamic state point without any temperature correction, the CG model possesses a rather favorable temperature transferability in a wide temperature range of 300-800 K at P = 1 atm and a good pressure transferability to some extent in a certain pressure range from 0.1 to 30 MPa. In addition to the local conformation and local packing distribution functions, the thermodynamic properties such as the glass transition temperature and the coefficient of linear thermal expansion are predicted correctly by the CG model, and the isothermal compressibility coefficients calculated from both atomic and CG models are on the same order of magnitude. Additionally, the stress-strain behavior under compression or tension of the CG model shows a qualitative agreement with the atomistic results, and the corresponding values of the elastic modulus of the CG model at different temperatures roughly match with those of the atomistic model.