Isocyanate-Free Polyurea Synthesis via Ru-Catalyzed Carbene Insertion into the N–H Bonds of Urea

Abstract

Polyureas have widespread applications due to their unique material properties. Because of the toxicity of isocyanates, sustainable isocyanate-free routes to prepare polyureas are a field of active research. Current routes to isocyanate-free polyureas focus on constructing the urea moiety in the final polymerizing step. In this study we present a new isocyanate-free method to produce polyureas by Ru-catalyzed carbene insertion into the N–H bonds of urea itself in combination with a series of bis-diazo compounds as carbene precursors. The mechanism was investigated by kinetics and DFT studies, revealing the rate-determining step to be nucleophilic attack on a Ru–carbene moiety by urea. This study paves the way to use transition-metal-catalyzed reactions in alternative routes to polyureas.

Diazirine-Functionalized Polyurethane Crosslinkers for Isocyanate-Free Curing of Polyol-Based Coatings

“…The linkage itself is naturally resistant to chemicals and solvents, and its self-hydrogen-bonding properties induce the organization of polymeric chains into microdomains, which improve the bulk properties of the material . Most isocyanate-free routes to PUR-like coatings are based on species such as carbonates, urethanes, and ureas. , In these aminolysis and transcarbamoylation reactions, polyurethanes are synthesized by generating the final urethane linkage in the polymerization step (Figure ). These isocyanate-free routes require catalysts and high temperatures, which can lead to side reactions forming urea, uretdione, isocyanurate, and allophanate linkages.…”

“… 3 Most isocyanate-free routes to PUR-like coatings are based on species such as carbonates, urethanes, and ureas. 4 , 5 In these aminolysis and transcarbamoylation reactions, polyurethanes are synthesized by generating the final urethane linkage in the polymerization step ( Figure 1 ). 6 These isocyanate-free routes require catalysts and high temperatures, which can lead to side reactions forming urea, uretdione, isocyanurate, and allophanate linkages.…”

Harnessing Activated Alkyne-Hydroxyl “Click” Chemistry for Degradable and Self-Healing Poly(urea vinyl ether ester)s

“…In the present state-of-the-art technology of PU production, it primarily relies on the reaction between diisocyanates and diamines. − This particular approach is afflicted with the disadvantage of isocyanates, which are widely recognized for their toxicity, raising concerns for health and safety. Furthermore, the method involves the use of raw materials, such as phosgene and chloroformates, which are associated with substantial environmental hazards and risks. , Hence, the pursuit of sustainable isocyanate-free routes for synthesizing PUs has gained considerable recent attention. − Urea, an inexpensive and nontoxic commodity chemical, has widespread application as a nitrogen source in fertilizers and serves as a crucial raw material in the chemical industry . The direct utilization of urea as a source of urea functionality in PUs represents an economically advantageous approach for their synthesis.…”

Self- and Cross-Fusing of Furan-Based Polyurea Gels Dynamically Cross-Linked with Maleimides

“…Herein, we focus on a polyurea (PU) formed by the reaction of a diisocyanate and diamine [ 37 , 38 ]. Molecularly, it is similar to polyamide, but has a structure where significant hydrogen bonding occurs between the polymer chains, enhancing the mechanical properties [ 39 , 40 ]. Recently, the use of PUs in films, foams, and composites, such as vertical body panels, spray foams, and microcellular foam liquid plastics, has attracted attention in industrial applications [ 41 , 42 , 43 ].…”