From CO2 to novel regioregular isocyanate-free poly(oxo-urethane)s

Abstract

Polyurethanes are a very important class of materials which finds applications in gasket sealers, cushioning and medical implants. The industrial synthesis of polyurethanes involve the use of phosgene and isocyanate compounds, noxious substances, which due to changes in REACH regulations tends to prohibition in the near future. An alternative for the synthesis of polyurethanes resides in the step growth polymerization of bis-cyclic carbonates with diamines. The cyclic carbonates can be prepared by the coupling of carbondioxide with epoxides, or diols. Polymerisation of the carbonates thus prepared, is non regioselective, and affords polyurethanes with primary or secondary alcohols, which favors side reactions and limits the molar mass of the polymer. A solution to this problem is the use of alpha alkylidene cyclic carbonates prepared by coupling CO2 with propargylic alcohols. Due to the high thermodynamic stability of CO2 a catalyst is required for the coupling reaction. Transition metal-based complexes, organic bases (guanidine, amidine, phosphine) and N-heterocyclic carbenes or olefins, have been proposed as catalysts. However they generally present sufficient activity at high pressure and/or temperature or require a high catalyst loading. Additionally some of them are toxic and/or sensitive to hydrolysis or oxidation. The objectives of this work was to develop new, efficient, and highly selective organo catalysts for the synthesis of cyclic carbonate monomers, and to prepare new non isocyanate polyurethanes using the monomers. We developed new, cheap, efficient organocatalyst, for the synthesis of a new bis-alpha alkylidene cyclic carbonate monomer. The bis-alpha alkilidene cyclic carbonate monomer was copolymerized with a diamine to afford a new regioregular poly(oxo-urethane).