Some criteria for the design of polyurethaneurea elastomers

Given the numerous variables in composition, reaction conditions, and processing, the design of a polyurethane elastomer with a specified set of properties is indeed a challenging task. The control of characteristics such as heat stability, toughness, fatigue, and other key qualities requires a compendium of theoretical and experimental knowledge. Optimizing a single property, e.g., low temperature resiliency, can necessitate changes in composition that may compromise other important properties. Thus, to balance the entire system in order to meet the specification limits, much more than an empirical approach is needed to achieve the goal in a reasonable time. In this presentation, we will demonstrate that, by use of an array of sophisticated testing methods and carefully designed experiments combined with computer modeling, the tailoring of a segmented elastomer can be placed on a scientific basis. Key methods of characterization are dynamic mechanical spectroscopy, small angle X-ray scattering, electron microscopy, Fourier transform infrared, and differential scanning calorimetry. Special experiments included the systematic synthesis and testing of a wide range of model compounds. Optimum soft segment properties such as chain length and mobility were defined. Hard segments that are properly segregated and have high thermal and mechanical integrity were synthesized and characterized. These and related experiments have led us to a better understanding of the molecular mechanisms underlying the mechanical and thermal behavior of an elastomer. With this knowledge we can select molecular components and control phase relationships in building elastomers to meet end use requirements that demand maximum static and dynamic polymer properties.