THERMAL AND MECHANICAL-PROPERTIES OF POLYURETHANE DIACETYLENE SEGMENTED COPOLYMERS .2. EFFECTS OF DIACETYLENE CROSS-POLYMERIZATION

Selective cross-linking of the hard domains of segmented polyurethanes via the radiationinduced solid-state reaction of diacetylene groups was utilized to ascertain the influence of hard domain cohesion and rigidity on the mechanical properties of these materials. The rigidity and mechanical integrity of the hard segment domains were found to play an extremely important role in determining their mechanical behavior. The specific influence exerted by the hard domains was found to be strongly dependent on molecular weight, the level and type of hard segment ordering, and the microstructure of the material. In all cases, the effect of diacetylene cross-polymerization was to increase the modulus and decrease the ultimate tensile strain. The ultimate tensile strength was found to initially increase, reach a maximum, and eventually decrease upon exposure to high-energy electrons. Disruption and reorganization of the hard domain system at high stress levels was verified as an important strengthening mechanism in segmented polyurethanes. © 1990, American Chemical Society. All rights reserved.