Molecular-Scale\nInvestigation of the Microphase-Dependent\nLoad Transfer Capability of Polyurethane

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