Recent Progress on the Non-phosgene Synthesis of Polyisocyanates
Polyisocyanates are important raw materials for military and civilian products such as solid propellants,adhesives,and coatings,supporting the rapid progress of modern industrial civilization.They are also important intermediates for drug synthesis,improving human health and well-being.However,the traditional syntheses of polyisocyanate are mainly through the reactions of polyamines with phosgene,which is highly toxic and harmful to the environment.In order to improve the green and low-carbon production from the source,promote harmonious coexistence between humans and nature,it is urgently necessary to innovate the synthesis path and develop green preparation technology for polyisocyanate.In recent years,the synthesis of isocyanates through non-phosgene methods has become a research frontier as an active intermediate for the synthesis of high-value-added derivatives.The latest progress in the non-phosgene synthesis of polyisocyanate is summarized through pathways such as dealchoholysis of carbonates through pyrolysis,Hofmann rearrangement of amides,Curtius rearrangement on acyl azides,Lossen rearrangement of hydroxamic acid,reductive carbonylation reaction on nitro compounds,N-substitution of cyanates,and so on.With the increasing requirements of circular economy for sustainable development,the syntheses of polyisocyanates and their corresponding polyurethanes through non-phosgene pathways will attract more attention in the future.
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