<i>In Situ</i> Synchrotron Radiation X-ray Scattering Evaluation of Domain Size and Spacing of Thermoplastic Elastomer under Elongation

Microphase separation occurs in polystyrene (PS)-b-poly(ethylene-co-butylene)-b-PS (SEBS), leading PS domains to serve as physical crosslinking points. To improve mechanical strength of SEBS, mechanical stability of PS needs to be clarified. Here, the molecular aggregation structure of SEBS films containing spherical PS domains packed in b.c.c. lattice was measured during stretching using in situ SAXS. During uniaxial stretching, a shift of structure factor reveals an increase in domain spacing in parallel to stretching direction while it decreased in the perpendicular direction. Affine deformation of all diffraction planes was observed, while they deviated from the trend above strain 5 equally. In the case of biaxial stretching, an increase in the domain spacing was observed in both stretching directions, indicating an isotropic deformation. Deviation from affine deformation of each diffraction plane was observed above strain 1.5, referring to the difficulty of maintaining the paracrystalline structures during biaxial stretching. Domain size of PS domains with polydispersity was determined from form factor using model calculation. From the change of radius, PS domains were proposed to deform to prolate and oblate spheroids during uniaxial and biaxial elongation, respectively.