Highly efficient isocyanate-free microwave-assisted synthesis of [6]-oligourea

Abstract

A new eco-friendly, isocyanate-free, energy-saving method for the production of [6]-oligourea, utilizing a green carbonylating agent, viz. propylene carbonate, is reported. It comprises an organocatalyzed, microwave-assisted, solvent-free synthesis. Two modes of microwave-assisted synthesis, viz. dynamic and fixed energy modes, were applied. Upon optimization, the dynamic mode gave 79% yields of [6]-oligourea.On the other hand, almost quantitative yields were obtained using the fixed mode, within 20 min, at 10 W and with the same catalyst loading. Combination of both organocatalysis and microwave energy input appears to be a key issue for the efficiency of the reaction, with the fixed energy mode being best suited. It should be noted that all data reported are reproducible (due to the homogeneous microwave technology used by CEM Discover S-Class of microwave reactors). To the best of our knowledge, this is the best eco-friendly synthetic approach for the preparation of the title oligomers.It paves the way for using more of the biorenewable and sustainable chemicals as a feedstock for the production of polyureas. The oligomer produced was analyzed by EA, ATR-FTIR, XRD, 1 H and 13 CNMR.Furthermore, thermal properties of the resulting [6]-oligourea were analyzed using TGA and DSC.

Utilization of carbon dioxide to build a basic block for polymeric materials: an isocyanate-free route to synthesize a soluble oligourea

“…10,11 As we know, traditional polyureas are usually produced based on the reaction of a diamine with isocyanates, 12-14 urea, [15][16][17] and diphenyl carbonate. 19 Moreover, it is possible to produce the feedstock of dimethyl carbonate and propylene carbonate from carbon dioxide with methanol and propylene glycol. These reactions are more environmentally friendly and energy-saving as they are operated in the absence of the toxic agents phosgene and isocyanates.…”

Solvent-free processes to polyurea elastomers from diamines and diphenyl carbonate

“…In addition, highly basic sodium methoxide was used for promoting the trans-esterification reactions. These deficiencies were confirmed in our laboratory [10] indicating that only low molecular weight of polyurea could be isolated due to subsequent product degradation [11].…”

[n]‐Oligourea‐Based Green Sorbents with Enhanced CO2 Sorption Capacity

“…[28] The dynamic synthesis mode was selected to reach mild temperatures and avoid excessive thermal microwavee ffects, which could disturbt he reactiony ield. [31] Under these conditions, equimolar amounts of homologous diamines and PC afforded the desired [n]-OUsa sw hite-colored powders upon drying.…”

“…Firstly,agradual decomposition occurs after 200 8C in all [n]-OUs, which can be explained by the formation of PC as ar esult of backbiting of the urethane end group. [28] Thermal stabilityo ft he backbone remains intact until about 300 8C, as observed in similarc ompounds. [32] As econd decomposition step was detected for all [n]-OUsa saresult of an arbitrary isocyanate formationr ather than backbiting or zip mechanism to form cyclic ureas (as in the case of oligomers with short methylene chains).…”

“…Recently,w er eported on an ecofriendly and quick approach for the synthesis of [6]-oligourea ([6]-OU). [28] This solvent-free methodi se asily conducted within minutes under mild microwave-assisted conditions along with propylenecarbonate (PC) as an ontoxic carbonylating agent. Due to the use of latter chemical, this approach shows minimal toxicityw hen compared to the other aforementioned carbonylating reagents.…”