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.