Origin of multiple melting endotherms in a high hard block content polyurethane. 2. Structural investigation

The structure and morphology of a set of high hard block content (50% to 100% hard segment by weight) linear thermoplastic polyurethanes has been investigated mainly via small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). All the results obtained in this investigation have been correlated to our previous work on the thermodynamic properties of the same set of samples (Saiani et al. Macromolecules 2001, 34, 9059). The soft segment was based on a poly(propylene oxide) polyol end-capped with ethylene oxide and the hard segment on a 4,4‘-methylenediphenyleneisocyanate (MDI) chain extended by 2-methyl-1,3-propanediol (MP−Diol). Samples with a hard segment volume fraction higher than 65% are shown to have a morphology consisting in soft phase domains embedded in a hard phase matrix. Alignment of the soft phase domains could be observed under specific preparation conditions. From our SAXS results, the same average interdomain distance was found for all the samples (di ≈ 15 nm). These ...