MORPHOLOGICAL BEHAVIOR OF SEGMENTED POLYURETHANE BLOCK COPOLYMERS (MDI/BD, SMALL ANGLE X-RAY, POLYETHER-BASED, DSC)

I. A series of polyether-based segmented polyurethane block copolymers is characterized by small angle x-ray (SAXS) and neutron scattering analyses. The materials contain hard segments formed from 4-4' diphenylmethane diisocyanate and butanediol, and range in hard segment content from 20 to 80 weight percent. Scattering results provide evidence for a transition from discrete to continuous microdomain morphology as the hard segment content is increased above ca. 40 percent by weight. The hard domain structure is found to be lamellar for all hard segment compositions. Measured interdomain spacings, specific interfacial areas, and electron density variances show that the hard segment sequences, though rigid, are not fully extended. The thickness of the hard microdomain corresponds roughly to 3 to 4 hard segment repeat units.;III. The microdomain structure and degree of phase mixing for the same series of copolymer prepared under different conditions are studied. By combining the DSC and SAXS results and applying thermodynamic relations between the soft microphase glass transition temperature and its composition, the individual microphase compositions for the hard and soft microphases are determined.;IV. The temperature dependence of mechanical properties for the series of polyether-based polyurethanes is investigated. Results from dynamic mechanical analysis indicate that a hard phase alpha relaxation peak, related to the hard phase glass transition process, is observed only after the sample has been heated above its highest melting temperature. Two alpha relaxation peaks are observed for samples with hard segment contents above ca. 30 weight percent confirming the existence of a two-phase morphology for these copolymers.;II. The thermal behavior of the same series of copolymers is studied in detail by Differential Scanning Calorimetry (DSC). Thermal annealing, quench mixing and isothermal crystallization studies are used to ascertain the morphological origin of the observed multiple endotherms. Three distinct endotherms are detected above the pure hard segment glass transition temperature and are attributed to the different hard microdomain structures.