Isocyanate-Free Approach to Water-Borne Polyurea Dispersions and Coatings.

Here, an isocyanate-free approach to produce polyureas from diamines and dicarbamates as monomers is reported. A side reaction limiting the molecular weight during the diamine/ dicarbamate polymerization, that is, N-alkylation of amine end groups, is investigated. Mitigation of the N-alkylation, either by enhancing the carbamate aminolysis rate or by substitution of dimethylcarbamates with more sterically hindered diethylcarbamates, affords polyureas with sufficiently high molecular weights to assure satisfactory mechanical properties. Stable polyurea dispersions with polyamines as internal dispersing agents are prepared, and the properties of the corresponding coatings are evaluated.