STRUCTURE-PROPERTY RELATIONSHIPS IN SEGMENTED ELASTOMERS: SMALL ANGLE X-RAY SCATTERING, THERMAL, AND MECHANICAL STUDIES

The structure-property relationships of a series of polyether and polyester polyurethanes and polyether-polyester segmented copolymers were studied as a function of hard-segment type, soft-segment type, segment length, hard-segment content, segment length polydispersity, and material thermal history. This research was organized as a series of four studies, each of which constitutes a separate chapter of the text.;Hard domains in the H(,12) MDI/BD-based materials are smaller than those in corresponding MDI/BD materials. Greater values for ultimate strength are found in the smaller domain H(,12) MDI/BD-based materials. Monodisperse distributions of hard-segment lengths produce smaller domains with better long-range order. Linear interfacial thicknesses for the MDI/BD and H(,12) MDI/BD-based polyurethanes were determined to be on the order of 15-35 (ANGSTROM) and 10-15 (ANGSTROM), respectively.;Shorter soft segment-based materials are more compatible than equivalent systems made with higher molecular weight macroglycols. Finally, polyether polyurethanes were shown to have more complete phase separation than equivalent polyester-based polyurethanes.;2. High Temperature Annealing Studies of Segmented Polyurethane Elastomers. A systematic study employing SAXS on the influence of high temperature (90(DEGREES) and 150(DEGREES)C) and annealing on the morphology of a variety of segmented polyurethanes is reported. Annealing improves the degree of phase separation in more compatible systems to a greater degree than in less compatible systems. Thicker interfacial regions are seen in the annealed material relative to the control. Increased interfacial mixing is apparent in the materials studied in situ at high temperatures.;1. Morphology and Properties of Short Segment Block Copolymers. A series of polyether and polyester polyurethane elastomers has been studied using differential scanning calorimetry, small angle x-ray scattering, wide angle x-ray diffraction, dynamic mechanical testing, infrared dichroism, and stress-strain experiments. 4,4'-Diphenyl methane diisocyanate/1,4 butane diol (MDI/BD)-based hard-segment materials were found to be semi-crystalline, whereas 4,4'-dicyclohexyl methane diisocyanate/1,4 butane diol (H(,12) MDI/BD)-based hard-segment materials were amorphous or slightly crystalline at best. The model presented for the morphology of the semi-crystalline polyurethane materials suggests cylindrical or parallelpiped-shaped hard-segment crystallites with low axial ratios. The crystalline domains contain chain folded MDI/BD segments oriented parallel to the cylinder axis surrounded by amorphous MDI/BD segments. The morphological model suggested for the H(,12) MDI-based polyurethanes involves spherical regions of amorphous hard segments possibly containing small crystallites of trans-trans H(,12) MDI/BD isomer at sufficiently high hard-segment molecular weights.;3. Small Angle X-Ray Scattering Studies of Heat Set Materials. SAXS studies of heat set (200-400% strain; 110(DEGREES)-125(DEGREES)C) segmented copolymers are reported. Hard-segment domain size and interfacial thickness were roughly twice as large in the direction of stretch than transverse to it in semi-crystalline materials. Amorphous materials showed no corresponding anisotropy in domain shape or interfacial thickness.;4. Annealing-Induced Morphological Changes in Segmented Elastomers. Thermal analysis has been used to study annealing-induced ordering in segmented elastomers. In general, annealing resulted in an endothermic peak at a temperature 20(DEGREES)-50(DEGREES)C above that of the temperature of annealing in both semi-crystalline and amorphous materials. This endotherm is ascribed to the disruption of domain structure resulting from the reorganization of lesser segment orders into more perfect arrangements upon annealing.