Multiblock Thermoplastic Polyurethanes: In Situ Studies of Structural and Morphological Evolution under Strain

The Influence of Long-Time Storage on the Structure and Properties of Multi-Block Thermoplastic Polyurethanes Based on Poly(butylene adipate) Diol and Polycaprolactone Diol

A series of semi-crystalline multi-block thermoplastic polyurethanes (TPU), containing poly(butylene adipate) (PBA), polycaprolactone (PCL) and their equimolar mixture (PBA/PCL) as a soft segment was synthesized. The changes in the physical-mechanical and thermal properties of the materials observed in the course of a 36-month storage at room temperature were related to the corresponding structural evolution. The latter was monitored using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXS) and mechanical tests (tensile strength test). The effects of the composition of the soft segment on the phase separation and crystallization of the soft segment were analyzed in detail. It was found that the melting temperature of the crystalline phase increases with storage time, which is associated with hindering of the phase separation of the hard and soft segments of the TPU samples as it was detected by FTIR.

Study on Mechanical Properties of Polyurethane Cross-Linked P(E-co-T)/PEG Blended Polyether Elastomer

To improve the mechanical properties of polyurethane cross-linked poly (ethylene oxide-co-tetrahydrofuran) (P(E-co-T)) elastomers at room temperature, using poly (ethylene oxide-co-tetrahydrofuran) and high-molecular-weight polyethylene glycol (PEG) as raw materials and polyisocyanate N100 as curing agent, a series of polyurethane cross-linked blended polyether elastomers were prepared by changing the elastomer-curing parameter R value (n(-NCO)/n(-OH)) and P(E-co-T)/PEG ratio. Equilibrium swelling measurements showed that the chemical cross-linkage of the elastomers tended to decrease with the decreasing R value, the average molecular weight (Mc) of the network chain increased, and the density of the network chain (N0) decreased. Wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) tests showed that PEG chain segments within the elastomers crystallized at room temperature, while the crystallinity increased with decreasing R value and increasing PEG content. The mechanical property tests showed that the elongation at break tended to decrease with increasing R value; the tensile strength first increased and then decreased. At R value 0.9, the elastomer presented good comprehensive mechanical properties. In addition, the mechanical properties of polyurethane cross-linked P(E-co-T)/PEG blended polyether elastomer showed an increasing trend with the increase in PEG content when the curing parameter of 0.9 remained unchanged.