Revealing the role of hydrogen bonding in polyurea with multiscale simulations

Typically, polyurea is a polymer forming microphase-separated structures. Various coarse-grained (CG) simulation models have been developed to study the microphase structure and viscoelastic properties of polyurea. However, since the hydrogen atoms were modelled implicitly in the existing CG models, the anisotropic hydrogen bonding between urea groups in the hard domain might not be treated properly. Here, we introduce a hybrid all-atom/coarse-grained (AA/CG) model for polyurea, the CGU model, in which atomistic resolution are preserved for the urea groups. This model is proven to reproduce the results of the AA model, despite 24 times faster to run. By comparing the traditional CG model and the CGU model, we found that hydrogen bonding leads to a head-to-tail arrangement of the urea groups and a significant slowdown of the hard segment dynamics. Non-equilibrium simulations of stress relaxation process indicate that hydrogen bonding causes a broad relaxation time spectrum, which is consistent with experiment results.