On the Versatility of Urethane/Urea Bonds: Reversibility, Blocked Isocyanate, and Non-isocyanate Polyurethane

The approach of the reversibility of isocyanate-based bond to all products of isocyanate chemistry, namely, urethane, urea, uretdione, biuret, allophanate, and isocyanurate, is reviewed. The high reactivity of the isocyanate group toward any nucleophilic compound promotes its reaction with both the reactant and the formed product from isocyanate/nucleophile reaction, if it is sufficiently nucleophilic. To obtain TP or cast PU elastomers, one or two diols can be reacted with the isocyanate. Phase separation is the essential parameter for controlling the final thermomechanical behavior for linear segmented TPU. These polymers offer unique possibilities for tailor-made materials through the variation of the block lengths and composition. Because isocyanate/alcohol and isocyanate/amine reactions are very fast, give no byproduct, and attain high degree of conversion, they are well suited for direct polymerization of two reactive liquids, A and B, in a mold.