A novel investigation on micro-phase separation of thermoplastic polyurethanes: simulation, theoretical, and experimental approaches

Thermoplastic polyurethanes (TPUs) based on soft segments with varying molecular weight and molecular architecture show interesting micro-phase separation, thermal, morphological, molecular dynamics, and rheological properties. In the present study, TPUs based on two types of polyols, i.e., poly(tetramethylene ether) (1000 and 2000g/mol) and polycaprolactone (500 and 2000g/mol), were synthesized. This work has aimed to combine synthetic procedures, physical-chemistry calculations, and molecular dynamics simulation to study the effect of structure and molecular weight of the soft segments on TPU properties. Extent and kinetics of micro-phase separation were quantified with several methods such as spectroscopy, time-sweep rheological analysis, product of interaction parameter and degree of polymerization (N), thermal analysis, compressible regular solution model, molecular dynamics, and microscopy. The results showed that high molecular weight polyether- and low molecular weight polyester-based synthesized TPUs have the highest and the lowest micro-phase separations, respectively. Moreover, in each class of polyol, the degree of micro-phase separation was concurrently increased with soft-segment block length. However, competition between enthalpic and entropic factors in the study of the polyols led to different results by various methods. Moreover, from the mechanical properties viewpoint, ester-based TPUs showed higher Young's modulus and lower elongation-at-break compared to ether-based counterparts.