TIT# Machine Prepared Thermoplastic Polyurethanes of Varying Hard Segment
     Content. Morphology and its Evolution in Tensile Tests
AUT# Stribeck, Almut; Jokari Sheshdeh, Farhad; P”selt, Elmar; Eling, Berend;
     in't Veld, Pieter J.; Goerigk, Gnter Johannes; Hoell, Armin;
SOU# J. Polym. Sci. Polym. Phys. (2015), doi:10.1002/polb.23742
LOC# xv149
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ABS# Machine-cast thermoplastic polyurethanes (TPU) are strained and monitored
     by small-angle X-ray scattering (SAXS). They are prepared from
     4,4'-methylene diphenyl diisocyanate (MDI), 1,4-butane diol (BD), and
     polytetrahydrofuran (PTHF1000). Upon stretching hard domains are
     destroyed. Most stable are the domains of materials with a hard-domain
     content (HSC) of 30%. Domain stability decreases with increasing HSC and
     crosslinking. Most materials show stability up to a strain 0.6. At higher
     strain the apparent long period decreases for the materials with HSC=30%.
     Correlated hard domains, the "strain probes" relax as others are
     destroyed. The fraction of relaxing probes and their ultimate relaxation
     decrease with increasing HSC. Chord distribution functions (CDF) computed
     from the SAXS exhibit the same sequence of static long-period bands. The
     band positions form a Fibonacci series, related to the underlying
     polyaddition process. This indicates a nearly quasicrystalline
     arrangement of stringed hard domains, identified as the strain probes of
     the discrete SAXS. At strains < 0.6 the probes experience half of the
     macroscopic strain, which reflects hard-domain rigidity.