Compositional effects were measured on a series of polyurethanes prepared by extending MDI-terminated PTMG prepolymers with dihydric alcohols and MCHDI-terminated prepolymers with diamines. The tensile and compressive stiffness and hysteretic loss increased while the resilience decreased with a decrease in the isocyanate equivalent weight of the prepolymer. Polyol chain extenders having an aromatic structure provided greater rigidity and increase in temperature on compressive cycling than did their aliphatic counterparts. Structural linearity and symmetry of both the aliphatic and aromatic extenders promoted greater rigidity and resiliency and less damping. Although direct replacement of MDI with MCHDI gives softer polyurethanes, use of the aromatic diamine extenders with the MCHDI-terminated prepolymers gave materials displaying the least resilience and greatest rigidity under static test conditions and the highest increase in temperature on compressive cycling. However, a significant increase in the chain length of the aromatic diamine-extended prepolymer provided properties quite similar to those obtained with the aliphatic diol systems.
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