Morphological Failure Mechanisms in Tensile Tests of Crosslinked Polyurethanes With Poorly Developed Domain Structure

Macroscopic failure of polyurethane materials of 30wt.-% hard-segment content is related to microstructure evolution mechanisms. Topology and functionality (f=2...4) of the polyols are varied. Samples are strained and small-angle X-ray scattering (SAXS) patterns are recorded. Only material PU-I (f=2) passes the tensile test. Material PU-Hs - a H-shaped (f=4) polyol with short arms - is not nanostructured. PU-Hl has long arms. It contains few hard domains placed at random. PU-Hl survives longer (strain: 1.8) than the other short-lived materials. Its isolated hard domains are not destroyed during straining. PU-X (f=4, star-shaped) develops microfibrils: one-dimensional (1D) correlations among hard domains, as deduced from a chord distribution function (CDF) analysis. PU-I and PU-Y are based on 2- and 3-functional polyols. They contain many well-separated hard domains with one-dimensional (3D) connectivity. Their arrangement of hard domains evolves identically, but not the population density. In PU-I (and PU-X) hard domains fail during straining, in PU-Y the interdomain soft phase density decreases.