Segmental Orientation in Well-Defined Thermoplastic Elastomers Containing Supramolecular Fillers

Abstract

The mechanical behavior of segmented block copolymers is studied by unraveling the deformation mechanisms on both a macroscopic and a molecular level. Small-angle X-ray scattering and infrared dichroism are used to study the deformation of a thermoplastic elastomer with bisureidobutylene hard segments (PCLU4U) containing various amounts of perfectly fitting supramolecular filler (U4U) incorporated. The pristine PCLU4U and polymers containing filler amounts up to 25 mol % show predominantly a shear type of deformation. The hard segment stacks tend to align parallel to the strain axis upon uniaxial deformation up to the yield point. Permanent deformation is caused by fragmenting of the stacks, which then start to reorient perpendicular to the strain axis. When >25 mol % of filler is added to PCLU4U, two hard phases are present: the first hard phase consists of polymer hard segments containing a maximum amount of filler incorporated and the second hard phase consists of filler aggregates only. In this case, all urea groups orient parallel to the strain axis when such a sample is uniaxially loaded up to the yield point. At the yield point, the first hard phase shows the same shear type of deformation as the pure PCLU4U polymer. The filler aggregates, however, are not connected to the soft segment matrix, and stress transfer to the soft matrix does not occur. Therefore, we propose that they remain parallel to the strain axis. All of these data support the unique character of the supramolecular fillers used in well-defined thermoplastic elastomers.