Macroscopic failure of polyurethane materials of 30 wt.-% 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.
Thermoplastic polyurethanes (TPUs) molded at 205, 215, and 235 °C are monitored by SAXS and WAXS during straining. A non-affine nanostructure deformation and related evolution mechanisms are found. DSC and microscopy are applied. DSC shows two melting endotherms. The results indicate that melts kept below the second peak stay phase-separated. The orientation parameter f(ϵ) and df/dϵ from WAXS are related to chain orientation mechanisms (strain ϵ). SAXS shows hard domains that are only correlated to a next neighbor (“sandwich”). Thick sandwiches lengthen more than thin ones. Thin-layer sandwiches feature a strain limit. Some are converted into thick-layer sandwiches. Two materials have tough hard domains. Material processed at 235 °C is soft and contains weak hard domains that fail for ϵ > 0.75.
