Fast-Tracking of the Segmental Orientation in Poly(ethylene oxide)-based Polyurethane Urea by Mechano-optical (Infrared Dichroism and Birefringence) Properties: Degree of the Soft-Segment Ordering Effect

Abstract

The orientation behavior of segment-specific chemical groups of NH and CH was investigated for poly(ethylene oxide) (PEO)-based polyurethane urea (PUU) during uniaxial stretching using a uniaxial stretching system integrated with spectral birefringence and ultrafast IR spectrometers that capture two polarization states simultaneously. PUUs with 30% by-weight urethane-urea hard segment content were prepared using PEO oligomers with number average molecular weights of 2000, 4600, and 8000 g/mol. High-molecular weight PEO-based PUUs exhibited microphase morphologies with sharp interfaces between the PEO matrix and urethane-urea hard segments, while low-molecular weight PEO-2000 (2000 g/mol)-based PUU exhibited a gradient interphase. This is primarily due to substantial hydrogen-bonding interactions between the urea hard segments and ether groups of highly amorphous PEO-2000 compared with highly crystalline soft segments in PEO-4600 and PEO-8000, which lack significant hydrogen-bonding interactions with urea groups and hence a sharper interface and improved microphase separation. The segment-specific chemical group orientation study revealed that the relaxation and reorganization behaviors are closely dependent on the initial morphology. In microphase-separated PUU with a gradient interphase, responses of the hard and soft segments to deformation are similar even at lower strain levels. For the microphase-separated PUUs with a sharp interface, the low-strain level orientation is localized in the soft-segment regions until the connection with the hard segments drive the orientation in the chain axis toward the stretching direction. This network transition is also reflected in the mechano-optical behavior as a change from a high-strain optical constant to a lower-strain optical constant.

Deformation‐Induced Photoprogrammable Pattern of Polyurethane Elastomers Based on Poisson Effect

“…During the axial stretching process, the Poisson effect exerts a significant influence on the polymer chains, the polymer chains undergo elongation along the stretching direction while simultaneously experiencing contraction in the vertical direction, [ 40–41 ] leading to a decrease in the interchain distance. [ 42–44 ] Simultaneously, the photodimerization of SAN induces crosslinking of the polymer chains, resulting in compressive stress in the vertical direction. This crosslinking leads to volume contraction in the exposed region, giving rise to the formation of surface microstructures.…”