ABSTRACT:Changes of structure and properties of segmented poly(urethaneura)s (SPUU) subjected to a sinusoidal strain were studied as a function of the duration of the load (the fatigue time). Mechanical experiments as well as infrared dichroism experiments indicate that destruction of hard segment domains and phase mixing between hard and soft segment domains proceed with increasing fatigue time. Infrared dichroism shows that the hard segments orient negatively, then positively, with increasing elongation. Negative orientation results from the behavior of the hard segment domain as a filler having an anisotropic shape ("domain orientation"). Subsequent positive orientation is explained by the hard segment orientation coupled with fragmentation of the hard segment domains ("segment orientation"). In the fatigue process, on the other hand, proceeding of phase mixing is dominant followed by phase demixing related to rearrangement and reorientation of the hard segments, which would finally lead to fracture. It is found that the fatigue process consists of three stages; the domain orientation stage, the phase-mixing stage, and the segment orientation stage.KEY WORDS Poly(urethaneurea) I Fatigue Mechanism I Infrared Dichroism I Spherulite Deformation I Segmented poly(urethaneurea) (SPUU) block copolymers are thermoplastic copolymers which have mechanical properties similar to those of conventional crosslinked rubbers. These materials belong to a class of (A-B)n type multiblock copolymers 1 -u consisting of alternately joined blocks of two chemically dissimilar segments along the polymer backbone, which are called hard and soft segments.Physical crosslinks are provided by the hard segments, which are generally formed from an extension of an aromatic diisocyanate with a low molecular weight diol or diamine. Elastomeric properties are imparted by the soft segments, usually formed from an aliphatic polyether or polyester macroglycol. Such SPUU is extensively hydrogen bonded. 3 -10 In all cases, the NH and C=O groups of each urethane or urea linkage can act as a proton donor and a proton acceptor. Although hydrogen bonding is an important structural feature of these materials, its influence on their properties and morphologies is not clear. In addition, two-phase microdomain structure 7 -10 • 12 • 13 has not been well understood due predominantly to the chemical complexity of the materials themselves. Charactensttc mechanical properties of SPUU, such as, high extensibility, and resiliency,
ABSTRACT:The fatigue mechanism of segmented poly(urethaneurea)s due to a sinusoidal strain was investigated from the structural point of view by means of small angle light scattering (SALS), small angle X-ray scattering (SAXS), and infrared dichroism (IRD) and was compared with the uniaxial deformation mechanism. The SALS patterns of the original sample films indicated the existence of a spherulite texture. There appeared a ring diffraction pattern in the SAXS photograph for the as-cast sample. The diffraction pattern came to have azimuthal angular dependence when stretched or fatigued; which was characterized by a defect in intensity in the stretching direction and a local concentration in intensity at the edge of the defect. Those indicated a selective destruction of the hard segment domain in the equatorial zone of the spherulite. The fatigued mechanism is proposed in order to account for the experimental results based on the spherulite deformation model. It was also found that samples having longer soft segments have higher degree of phase separation at the beginning and that these mechanical properties and orientational behavior are less sensitive to fatigue time.KEY WORDS Poly(urethaneurea) I Fatigue Mechanism I Spherulite Deformation I Infrared Dichroism I Small Angle X-Ray Scattering I Small Angle Light Scattering I Segmented poly(urethaneurea)s (SPUU) and segmented poly(urethane)s (SPU) have been considered for use as high performance elastomeric materials. The unique mechanical properties of SPUU and SPU result from their heterogeneous microdomain structure composed of the hard and the soft segments. Hydrogen bonding also plays an important role in its properties. Structures of SPUU has been extensively studied in terms of DSC, infrared dichroism (IRD), small angle X-ray (SAXS) and neutron scattering (SANS) techniques.1 -? Kimura et a/. 1 · 5 utilized small angle light scattering (SALS), SAXS, and IRD and studied the deformation mechanism of SPUU. They found a spherulitic structure in SPUU and explained the deformation mechanism of SPUU by the analogy of the deformation mechanism of crystalline polymers, e.g., polyethylene. Bonart et a/. 8 • 9 proposed a different model of deformation on segmented poly(urethane) (SPU), which is based on rotation of a particle having an anisotropic shape in a flow field (domain orientation) followed by segment orientation. The deformation mechanism of SPUU and/or of SPU is, however, still an open question. This fact is partially due to the complexity of the microdomain structure of SPUU and SPU. It is clear that ·the deformation mechanism depends on the chemical structure of SPUU or SPU.Desper et a/. 10 proposed three possible models of deformation: a shear model, a tensile model, and a rotation or translation of inde-1067
ABSTRACT:Infrared (IR) dichroism study of segmented polyurethaneurea (SEUU) with ABA type triblock copolymer as a soft segment was carried out, where A stands for poly(oxyethylene) (PEO) and B stands for poly(oxytetramethylene) (PTMO). IR dichroism analysis of SEUU films under elongation suggested that the introduction of PEO units to the ends of PTMO brought about more aggregation of the hard segments, i.e., the better microphase separation in SEUU than segmented polyurethaneurea (SPUU) prepared from PTMO. Under uniaxial extension, the crystalline hard segment domain oriented transverse to the stretch direction at early stage, the degree of orientation being larger with the increase of PEO content. The larger was the PEO content, the better the microphase separation in SEUU.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.