Molecular-Scale Investigation of the Microphase-Dependent Load Transfer Capability of Polyurethane

In this study, we investigated the mechanism by which the microphase structure of polyurethane (PU), manipulated by the chemical composition, determines its macroscopic mechanical properties. Increasing the hard segment content induced a microphase transition from globular to elongated to bicontinuous. This transition significantly altered the mechanical behavior of PU from hyperelastic to elasto-plastic. This enhancement in the mechanical properties was related to the load-transfer capacity of the hard domains in each microphase. In the globular phase, most of the strain energy was absorbed by the soft matrix, limiting the contribution of the hard phase to the mechanical properties. Conversely, elongated discontinuous structures facilitated a homogeneous strain distribution during tension, promoting an immediate load transfer to the hard domain. To quantitatively evaluate the load-transfer efficiency, a mechanical model in which one soft hyperelastic spring was coupled to two rigid elasto-plastic springs was considered. The effects of the microphase morphology and hard domain dissociation on the load-transfer capability were identified. This study contributes to a molecular-level understanding of the deformation behavior and mechanical response of microphase-separated PU.