MICROSTRUCTURE OF SEGMENTED AMORPHOUS POLYURETHANES - SMALL-ANGLE X-RAY-SCATTERING AND MECHANICAL SPECTROSCOPY STUDIES

The microstructure of polyurethanes and its evolution upon thermal tre atment were investigated by means of small-angle X-ray scattering and low-frequency high-resolution mechanical spectroscopy. The segmented c opolymer materials studied in this work were prepared in bulk and were completely amorphous as a consequence of the chemical composition of the soft and hard segments. This amorphous state results in model mate rials and, in principle, easier interpretation of the morphology from experimental results. It is shown in this work that thermal treatment induces a coarsening of hard-phase microdomains and an increase of the interfacial region, which remains of the order of a few angstroms. Th is morphology evolution leads, to some extent, to a weakening of the m echanical properties as observed above the glass transition temperatur e of the soft-phase matrix. The conclusion is that the synthesis condi tions, as well as subsequent heat treatment, are to be carefully consi dered in order to obtain materials with well controlled physical prope rties.