Polyurethane elastomers, polyurethaneurea elastomers, and polyurea elastomers differ in their composition and properties.
Polyurethane elastomers are formed by reacting oligomeric diols or triols, diisocyanates, and small molecular weight polyols. These raw materials do not contain amine-based compounds. The elastomer can be prepared through a one-step or a prepolymer method.
Polyurethaneurea elastomers are obtained by first reacting oligomeric diols or triols with diisocyanates to form a prepolymer, which is then solidified by further reaction with an aromatic diamine chain extender. The resulting elastomer contains both urethane and urea groups. While strictly speaking, it falls under the category of polyurethaneurea, it is generally classified as polyurethane.
Polyurea elastomers, on the other hand, are typically produced by directly reacting amino-terminated polyethers (such as polyether diamines or polyether triamines) with diisocyanates and aromatic diamines. Due to the rapid reaction between the amino and isocyanate groups, a spray molding process is used for their preparation.
It's worth noting that if a mixture of amino-terminated polyether and aromatic diamine reacts with an isocyanate-terminated polyurethane prepolymer during spray molding, the resulting material is not a pure polyurea elastomer, but a polyurethaneurea elastomer, as there are carbamate groups present in its molecular chain.
Polyurea elastomers, with their higher urea group content, exhibit greater polarity and are capable of forming more hydrogen bonds. As a result, they generally have higher modulus and strength compared to polyurethane elastomers.