Change in Hierarchical Structure of Segmented Polyurethane Elastomers under Mechanical Deformation

Polymer materials possess a hierarchical structure such as orientation, conformation, crystal structure, microdomain structure, and so on. When external stimulus is applied to polymers, these various structures would respond depending on the size. In this study, lattice strains obtained from the crystal structure of hard segment domain and microphase-separated structure of segmented polyurethane (SPU) elastomers were evaluated under mechanical deformation by wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) measurements. SPU elastomers were synthesized with poly(oxytetramethylene) glycol, trans-1,4-bis(isocyanatomethyl) cyclohexane (1,4-H₆XDI), and 1,4-butanediol. Change in molecular aggregation structure of the SPU with 20 and 30 wt% hard segment contents were investigated. Both strains (e_SAXS and e_WAXD) obtained from SAXS and WAXD linearly increased with increasing strain. Compared to HX-20, HX-30 exhibited larger e_SAXS and e_WAXD in both deformation modes. This is because strain can be easily propagated to whole samples due to well-developed hard segment domains formed in HX-30. e_SAXS and e_WAXD values obtained by biaxial deformation were larger than for uniaxial one, indicating that the biaxial deformation produces severer condition to the samples.