Microphase-separated Structure and Rheological Properties of Polyurethanes

Abstract

A novel diisocyanate, 1,2-bisisocyanate ethoxyethane (TEGDI) whose backbone is ether bonds, was used for the preparation of polyurethane elastomers (PUEs). Highly softened TEGDI-based PUEs were successfully prepared on account of flexibility of TEGDI itself and weaker phase separation. A relationship between conformation and molecular mobility of the soft segment were investigated using dynamic viscoelastic measurement. The peaks of α relaxation of the soft segment chains were clearly observed in the loss tangent (tan δ) curves at various strains. The onset temperature of α relaxation decreased with increasing strain. This result indicates that the size of cooperative motion of the glass transition decreased due to the orientation of the soft segment chains with increasing strain. The effect of the microaggregation structure on the rheological properties of thermoplastic polyurethane (TPU) were investigated. The TPUs showed the strain hardening of uniaxial elongation viscosity with increasing annealing temperature owing to residual hard segment domains at an operating temperature. It was revealed that the formation of well-organized hard segment domains had a profound effect on the rheological properties of TPUs, in particular on their elongational viscosity. © 2008 The Society of Rheology, Japan.