Ternary phase separation in polyurethane elastomers with immiscible soft segments

Polyurethane elastomers with two immiscible hard-segment polyols have been synthesized from homogeneous prepolymer mixtures, to obtain incompatibility on a molecular scale from reaction driven phase separation. Miscibility of a series of different soft-segment polyols and of their prepolymers with 4,4'-diisocyanatodiphenyl methane (MDI) has been investigated by cloud point analysis. UCST-behavior was observed for all binary combinations of polyols and of prepolymers; prepolymer formation lowered UCST with respect to polyols with the option to adjust it by further addition of MDI. Polyurethane elastomers have been synthesized and characterized with respect to their thermal, mechanical and viscoelastic (DMTA) behavior. Broad temperature ranges of loss factor above 0.1 were observed from polyurethanes with two immiscible soft-segment polyols. Rebound resilience, however, was still significant at room temperature, because of the low transition temperatures of the polyols used. Introduction of a third partially miscible component, a hard-segment from tetraethyleneglycol and MDI gave materials with a loss factor above 0.1 over a temperature range from -50 to 120 degreesC and higher. The studies proved that the concept of intimate mixing of immiscible soft-segments in polyurethanes works for the design of viscoelastic materials with good damping properties.