Polyurea Elastomers

Some novel polyoxyalkyleneamine with specific structure and high reaction activity used in sprayed polyurea elastomer have been synthesized. There are two steps in the synthesis: A) Diketene and polyols react to obtain polyfunctional acetoacetic esters as intermediate B) Polyfunctional acetoacetic esters react with aliphatic or aromatic monoamines or polyamine to the corresponding polyfunctional amino-crotonates. The condition of the reaction has been selected.A number of polyurea elastomer coatings have been explored in this study, and the results have highlighted the impact that some key formulation and processing variables impart on elastomer properties. Reaction times were tailored via the incorporation of secondary amine-containing chain extenders. Accordingly, it was demonstrated that the gel- and tack-free times for a specific system can be extended by almost ten and over thirty seconds, respectively. The effect of system index upon elastomer physical properties was also probed. Analyses of the corresponding free-film elastomers showed that indices above 1.05-1.10 gave the highest elastomer properties while these same attributes fell off sharply atindices below 1.00. The most influential aspect of polyurea formulation was determined to be %NCO value of the quasi-prepolymer utilized. This study demonstrated the concept that properties such as hardness, tensile strength, elongation, and tear strength can be manipulated through the use of varying %NCO levels. Generalizations of these underlying relationships are offered, where prudent, to help guide the design of polyurea spray elastomers for various application areas.In this paper, the effects of specific parameters on the final properties of polyurea spray coatings are also reported, specifically: the influence of varying the mixed isomer composition on the cure speed and film properties; the influence of slow-reacting reagents on the film properties; and the influence of the functionality of the isocyanate prepolymer and the resin blend on cure speed, cure efficiency and film properties.Recent studies have revealed that aromatic isocyanates with a high 2,4'-MDI isomer content do impart steric disruptions 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 observed by using these high 2,4'-MDI isomers versus similar polyurea systems that utilized isocyanates with lower 2,4'-MDI isomer 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'-MDI products.