High molecular weight multifunctional fluorescent polyurea: Isocyanate-free fast synthesis, coating applications and photoluminescence studies

Isocyanate-free synthesis of high molecular weight polyurea (PUrea) is a challenging and important area of research, considering the health and safety concerns related to isocyanates and a wide range of day-to-day uses of polyurea. In this article, an isocyanate and phosgene-free synthesis of high molecular weight fluorescent polyurea (Mn > 150,000) is reported via triazolinedione (TAD)-indole click reactions. Both the bisTAD and bis-indole monomers are synthesized from diphenyl carbonate using solvent-free reactions. The synthesis of polyurea is finished within 15 min under ambient conditions, without the use of any additives and catalysts, which is a remarkable advantage in comparison to all other reported methods in the literature. The molecular weight (Mn) of the polyurea can be defined as either very high molecular weight >150,000 g/mol or low molecular weight ∼ 3500–4000 g/mol via choosing a suitable solvent for the polymerization reaction. This approach is also useful for polyurea-based hydrophobic coatings as evidenced by the water contact angle analysis. The indole-derived aromatic moieties introduced within the polymer backbone; impart photoluminescence properties and polymers show excitation-dependent emission behavior.