ABSTRACT
Polyurethane elastomers are a commercial success because of their broad range of properties, low cost, and ease of production. Nonetheless, developing new, less expensive polyurethane elastomers with improved or expanded properties is an important goal. Since hard domains dominate the physical properties of these polymers, we have investigated methods to disrupt hard domain formation. The use of multiple chain extenders was envisioned to inhibit hard domain formation by disrupting the alignment between hard segments. In MDI-based polyurethanes, we observed up to a one magnitude reduction in tensile modulus and a significant increase in elongation compared to polymers containing a single chain extender. The stress relaxation of these polymers containing mixed chain extenders is lower than the control polymers, and there was no loss of high temperature properties when multiple chain extenders were used. Furthermore, as the mole fraction of either of the two chain extenders is increased from 0.5, the properties of the resultant polymer approach those of the polymer with that particular pure chain extender. Polymers containing TDI or HDI as isocyanate do not have such a dramatic drop in modulus when multiple chain extenders are used. HDI polymers are too strongly phase separated to significantly alter the morphology. TDI polymers produced with a strongly hydrophilic soft segment are not phase separated, while in less polar polyols the two isomers in TDI may effectively disrupt hard domain formation independently of the chain extenders. Nonetheless this technology is a simple and cost effective method for tailoring MDI-based polymers’ properties over a wide range by only minimally changing the formulation.
