Systematic Coarse Graining of a High‐Performance Polyimide

Abstract

An important high‐temperature polyimide, namely HFPE‐30, has been coarse grained to three different levels of detail. It has been shown that while it is possible to successfully calibrate bonded and non‐bonded forcefields and attain realistic densities with all levels of coarse graining, reproducing chain structures and dynamic properties requires an adequate level of atomistic detail to be retained. A model that coarse grains the HFPE‐30 molecule into eight beads, approximates both chain structure and dynamic properties well. Alternately, the unrealistically fast dynamics in coarse‐grained models can be slowed down by increasing the thermal coupling constant by a scaling factor that is estimated by comparing mean square displacements in detailed atomistic and coarse‐grained simulations. In general, stress‐strain responses of coarse‐grained systems do not match those of the detailed atomic systems except when the coarse graining involves eight beads. In cases where lesser number of beads are used, slowing the dynamics down by the estimated scaling factor takes the stress‐strain response of the coarse‐grained system close to that of the detailed atomistic one.