Toward polymers with oxazolidin-2-one building blocks through tetra-n-butyl-ammonium halides (Cl, Br, I) catalyzed coupling of epoxides with isocyanates

Abstract

The selectivity of the reaction of 4,4-methylene diphenyl diisocyanate MDI with o-cresyl glycidyl ether OCGE yielding oxazolidin-2-one and isocyanurates, and applying tetra-n-butyl ammonium halide as catalysts is higher in the order chloride, bromide, iodide. The dominant reaction pathways were inferred from the reactivity of the system with various ratios of MDI to OCGE, and using IR spectroscopy to monitor the progress. The reaction proceeds in several steps with initial nucleophilic attack of the halide on the epoxide yielding an alkoxide intermediate. The alkoxide reacts with isocyanate to yield a carbamato intermediate that may either ring close to form oxazolidinone or catalytically form isocyanurates by addition of more isocyanate and backbiting. The formation of isocyanurate is the reaction with the lowest activation barrier. Isocyanurate acts also as an isocyanate precursor as it is ring opened by the alkoxide intermediates in a slower consecutive process. Oxazolidinone modified epoxy prepolymers could be prepared from bisphenol A diglycidyl ether and MDI.