Multiscale Simulation of Multicomponent Polyurethane Elastomers: Unraveling Composition-Dependent Microphase Separation Dynamics and Mechanical Properties

The performance of multicomponent polyurethane elastomers is governed by their microphase-separated morphology, which arises from a complex interplay between intermolecular interactions and thermodynamic incompatibility. Unraveling this relationship is particularly challenging in systems with bi-incompatible soft segments, such as polydimethylsiloxane (PDMS) and polycarbonate diol (PCDL). Here, we present a bottom-up multiscale simulation framework that integrates density functional theory (DFT), all-atom (AA) molecular dynamics, and a reactive coarse-grained (CG) system to dynamically simulate the entire process, from prepolymerization to microphase separation. Our DFT calculations quantify the superior hydrogen bonding capability of urea and urethane groups and confirm the pronounced incompatibility between the soft components. These quantum derived insights informed the charge assignment in the AA simulations via the restrained electrostatic potential (RESP) method, and the resulting structural correlations were subsequently transferred to the mesoscopic scale through iterative Boltzmann inversion (IBI). Finally, a reactive CG system was obtained by incorporating a chemical bond formation algorithm, which can accurately capture various interactions and demonstrate that the aggregation of hard segments and the thermodynamic incompatibility of soft segments dictate the evolving microphase morphology. By systematically varying the ratio of each component, we precisely control structural transitions from dispersed to bicontinuous and island morphologies, which directly correlate with mechanical properties. This work not only provides fundamental insights into the microphase separation dynamics of complex polyurethanes but also establishes a predictive platform for the customized design of high-performance polyurethane elastomers.