Performance and Processing Enhancements of Aromatic Polyurea Elastomer Systems Prepared from High 2,4′-MDI

Polyurea elastomer systems have been formulated to produce high performance, rapid curing coatings and caulks that can be applied in adverse climates that would normally inhibit the use of other conventional chemistries. It is the inherently rapid reaction rate of isocyanates and amines that allows for the unique gel and cure rates that enables the consistent application of polyurea elastomers over a broad temperature and humidity range. These fast reaction rates, though favorable to the experienced applicator, can be an initial challenge to those who are new to this technology. In an effort to reduce the reaction rates of these polymer systems, sterically hindered amines and isocyanates have been examined. Recent studies have revealed that aromatic isocyanates with a high 2,4’-isomer MDI content impart steric hindrance that effectively reduce the reaction rates of typical polyurea spray coatings and dual-syringe applied polyurea caulks. The longer open times of these systems allow for reductions in processing pressures and temperatures of the plural component spray machines typically used for polyurea spray applications. The extended processing time also leads to elastomers with improved flow, leveling, and adhesion to a variety of substrates. In addition, significant performance enhancements of tensile strength, tear strength, elongation, and modulus of the resulting cured elastomers have been obtained by using these high 2,4’-isomer MDI versus similar polyurea systems that utilized isocyanates with lower 2,4’-isomer MDI content. This presentation illustrates the physical properties and processing enhancements of polyurea spray coatings and dual-syringe applied polyurea caulk products that are achieved using these new, high 2,4’-isomer MDI products.