Structure and Properties of Fatigued Segmented Poly(urethaneurea)s II. Structural Analyses of Fatigue Mechanism

Abstract

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

Structure and Properties of Fatigued Segmented Poly(urethaneurea) I. Segment Orientation Mechanism due to Fatigue

“…This is a kind of "domain orientation" proposed by Hashimoto et a/. 25 in the case of deformation of block copolymers. In Stage III, the spherulites are completely broken except at the polar region and then rearranged and reaggregate to a fringed-micell-like structure parallel to the stretching direction ("segment orientation") resulting in increases of the modulus and the cohesive force index.…”

“…In the case of TM-1 and TM-3, spherulitic structures were found in the thick film with small angle light scattering technique, 25 but not in the thin film. This may be simply due to .. the low optical contrast between the spherulites and the matrix.…”

“…All of these are supported by the small angle light and X-ray scattering analyses which will be reported in the forthcoming papers. 25 …”

Structure and Properties of Fatigued Segmented Poly(urethaneurea)s III. Quantitative Analyses of Hydrogen Bond

“…A 1 (1665) + A 1 (1638) + A 1 (1633) (2) where A 1 (x) represents integrated absorbance having a maximum at x (cm-1 ), and HuT and HuA denote the indices of hydrogen bonds of urethane and urea groups, respectively. It should be noted that these indices do not mean exact fractions of hydrogen bonds because the extinction coefficient of neither free or hydrogen bonded carbonyl groups has been precisely evaluated.…”

Small angle x-ray study of the deformation of 4,4'-diphenylmethane dilsocyanate1, 4'-butanediol (MDIBDO) based polyurethanes

“…Crazes have been observed at elongations close to failure in all three polyurethanes studied so far, yet the presence of crazing has not been recognized in the scientific literature as being important Small angle x-ray scattering of polyurethanes has been studied by numerous authors [1,7,8,[12][13][14][15][16][17] but only a relatively small number of these were concerned with morphology changes that occurred with deformation [15][16][17].…”