Coordinative Ring‐Opening Polymerization of Limonene Carbamate Toward Phosgene‐ and Isocyanate‐Free Polyurethane

Abstract

Abstract This study presents a phosgene‐ and isocyanate‐free route for the synthesis of polyurethanes using ( R )‐limonene as a bio‐based starting material. The synthesis of the cyclic limonene‐based carbamate monomer LU is achieved in high yields using dimethyl carbonate as a sustainable, less hazardous phosgene surrogate and is verified by NMR, SC‐XRD, ESI‐MS, GC‐MS, and elemental analysis. Polymerizations were carried out by coordinative ring‐opening polymerization. Sn(Oct) 2 showed the best catalytic performance, achieving up to 93% conversion with molecular weights up to 16.0 kg mol −1 at a polydispersity of 1.5. Detailed mechanistic insights were obtained by kinetic studies, end group determination via ESI‐MS and stoichiometric ninhydrin experiments, N – H methylation of LU , kinetic isotope experiments, and 119 Sn NMR measurements. The resulting semi‐crystalline polyurethane exhibits promising thermal properties, including a decomposition temperature of 252 °C and a glass transition temperature above 150 °C. Depolymerization in solution was achieved in high yield using the same catalyst. This work describes a coordinative ring‐opening polymerization approach using a terpene‐based carbamate as monomer, an important step toward bio‐based polyurethanes.