Sustainable block copolymers of poly(limonene carbonate)

Abstract

Poly(limonene carbonate) (PLimC) is a bio-based, non-food-based polymer produced by copolymerization of limonene oxide (LO) with carbon dioxide (CO₂). It can be a potential candidate for the replacement of toxic state-of-the-art polycarbonates only after improvement of its mechanical properties. An elegant way to tune and improve the mechanical properties of PLimC lies in copolymerization. For this, we present the basic studies regarding the copolymerization behaviour of LO/CO₂ with the lactide monomer and its derivatives using a catalyst [(BDI)Zn-(μ-OAc)]. The simultaneous copolymerization of LO/CO₂ with lactide in one pot did not provide a random copolymer. Advanced characterization methods were used to study the polymer structure, and it was proved to be a block copolymer (poly(limonene carbonate)-block-poly(lactide) (PLimC-b-PLA)) with inhomogeneous macromolecular chain compositions. A sequential living ring-opening copolymerization method provided precise block copolymers. The mechanical characteristics could be altered by the use of lactide derivatives with a low glass transition temperature. The use of lactide with long hexyl alkyl chains during sequential copolymerization provided block copolymers with polyester soft blocks with a very low glass transition temperature (T_g = −38 °C) showing rubber-like behavior. Upscaling of the method, processing and detailed characterization of the mechanical properties will be carried out in the future based on the present work.