Terpolymers derived from Limonene Oxide and Carbon Dioxide: Access to Cross-Linked Polycarbonates with Improved Thermal Properties

The formation of bio-derived materials is gaining momentum in academic and industrial research as a consequence of depleting petroleum resources, providing mid- and long-term alternative sustainable materials. In this context, we have prepared a series of terpolymers derived from the renewable terpene limonene producing polycarbonates with a controlled and variable ratio of incorporated nonfunctional cyclohexene oxide (CHO) and functional limonene oxide (LO) monomers. As catalyst, a simple binary combination of an Al(III) aminotriphenolate complex and PPNCl (PPN = bis(triphenyl)phosphine–ammonium) has been used to afford the targeted, partially bio-based polycarbonates with typically high carbonate content (>95%), good conversions, and a controllable amount of olefinic groups in the terpolymer backbone. Cross-linked polymers (CLP) have been easily obtained from these terpolymers through thiol–ene click reactions allowing for the preparation of interconnected networks with improved thermal properties with their T_d in the range of 250–280 °C and with glass transitions (T_g) of up to 150 °C. A detailed analysis of the cross-linked polycarbonates demonstrates a clear relation between the percentage of potential cross-linking groups in the terpolymer precursors and the physicochemical properties including solubility, rigidity, and thermal stability.