Structures of Hard Phases in Thermoplastic Polyurethanes

Limited long-range
ordering and the presence of both hard and soft
segments can cause substantial difficulties for structure determination
in urethane elastomers. Here, the structuring has been investigated
for a series of thermoplastic polyurethanes composed of 4,4′-methylene
diphenyl diisocyanate and 1,4-butanediol. We utilize pair distribution
function analysis of X-ray total scattering measurements to directly
access the local structure and quantify the degree of ordering, showing
that the structure varies significantly over the range of different
component ratios investigated. A simple method is demonstrated for
evaluating the viability of various structure candidates for the hard
segment. The nature of the molecular conformations and packing is
verified, allowing both ordered and disordered components to be quantified
through structural modeling.