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

Abstract

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 2000 g/mol) and polycaprolactone (500 and 2000 g/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 (χN), 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.