(740g) Molecular Simulation of Thermoplastic Polyurethanes Under Large Mechanical Deformation

Analysis of the effect of topological features at the inter-domain surfaces within a heterogeneous polymer on its mechanical behavior is important to understand and design these materials for various applications, yet such detailed analysis remains elusive so far. In this study, using atomistic Monte Carlo and molecular dynamics simulations, we reveal how the interphase topology affects the mechanism of mechanical deformation for a set of thermoplastic polyurethanes (TPUs). TPUs are versatile polymers that have rigid and flexible segments that segregate on the nanometer length scale into hard and soft domains that are coupled mechanically through prolific interfacial zones between regions of differing compliances. Using a Monte Carlo method originally developed for semicrystalline polymers, we construct a detailed, thermodynamically rigorous, atomistic model of the interfacial zone between hard and soft domains within a TPU, with realistic distributions of bridges, loops and tails. We then deform these structures using nonequilibrium molecular dynamics simulations, identify the evolution of important topological features such as bridge during mechanical loading, and correlate the molecular behavior to system observables like yielding, plastic flow and toughing. We have found several distinct mechanisms of mechanical deformation, depending on the categories of interphase topology and loading directions.