Explorations into the sustainable synthesis of cyclic and polymeric carbonates and thiocarbonates from eugenol-derived monomers and their reactions with CO2, COS, or CS2

Abstract

Polymers obtained utilizing renewable monomers (bio-based polymers) have attracted much attention recently due to their intrinsic ability to address environmental issues and depletion of fossil fuels, which are the main drawbacks of oil-based polymers. Herein we report the synthesis of a novel renewable eugenol-based epoxide from the natural product eugenol and an examination of its coupling reactions with CO₂, COS and CS₂ using a well-defined binary (salen)CrCl/PPNCl catalyst system. We have observed that the coupling reactions of eugenol epoxide with CO₂ and CS₂ preferentially lead to the formation of cyclic products, whereas reactions with the reactive COS monomer lead to the formation of polymonothiocarbonate polymers in a regioselective manner at room temperature. On increasing the reaction temperature both cyclic and polymeric products were obtained. Furthermore, an eugenol based thiirane was synthesized and its copolymerization reactions with CO₂ and COS were unsuccessful. All the cyclic and polymeric products were characterized by different spectroscopic and analytical techniques, and the molecular structures of the renewable monomers and their cyclic products were established by using single crystal X-ray diffraction studies. Thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC) studies of the polymers reveal that the polymonothiocarbonate polymers are quite stable up to 200 °C and have high glass transition (T_g) temperatures (75 °C), which makes these polymers of interest for some applications.