Coarse–grained molecular modeling of the microphase structure of polyurea elastomer

Abstract

We present a structure–matching coarse–grained model of polyurea, similar to united atom models, in which hydrogen atoms are implicitly represented. The model was trained using iteration Boltzmann inversion and a new heuristically–determined, distance–dependent scaling function that dramatically reduces the iterations required. With its reduced complexity and accelerated dynamics, the coarse–grained model can simulate microphase separation with hard domain spacing of 5 nm, comparable to x-ray scattering measurements of similar polyurea elastomers. An analysis of the morphology of two model systems shows a large, interconnected hard domain within a multiblock system, compared to an interrupted hard phase composed of separate smaller ribbon–shaped domains in a diblock system. To analyze the topology of soft segment connectivity, we calculated their end–to–end distribution, revealing that soft segments are composed of a large population of bridge–like segments and a smaller population of loop–like segments.