Thermoplastic polyurethanes are type AB co-polymers with randomly alternating hard and soft segments. The soft segments, consisting of long polymer chains of one macroglycol (polyether or polyester type), are flexible and weakly polar. The hard segments, obtained by the reaction of the isocyanate and the chain stretcher (for example 1,4-butanediol), are rigid and highly polar. The thermodynamic incompatibility of hard and soft segments at lower temperature generates a polyphasic structure. This structure is what gives thermoplastic polyurethanes their special properties. In specific terms, the hard segments act as cross-linking units while the soft phase gives the material its flexibility.

Rheological measurements are used to monitor the transition phase of thermoplastic polymers in quantitative terms. The changes in the polymer microstructure are also induced by well-defined thermal histories. The combined use of rheological and thermometric experiments thus serves as useful tools for characterising the transitional behaviour of thermoplastic polymers. Measurements like these are at the basis of Chiorino’s highly successful MATERIAL-PROCESS-PRODUCT chain.