(+)-Limonene-Lactam: Synthesis of a Sustainable Monomer for Ring-Opening Polymerization to Novel, Biobased Polyamides

In this work, the synthesis of limonene lactam starting from limonene epoxide and its subsequent ring-opening polymerization (ROP) to novel polyamides is presented. Sustainable, biobased materials are gaining interest as replacements of conventional, petroleum-based materials, and even more important, as high-performance materials for new applications. Terpenes-structurally advanced biobased compounds-are therefore of great interest. In this research, limonene lactam, a novel biobased monomer for preparing sustainable polyamides via ROP, can be synthesized. Limonene lactam possesses an isopropylene and a methyl side group, thus stereocenters posing special challenges and requirements for synthesis, analysis and polymerization. However, these difficult-to-synthesize structural elements can generate novel polymers with unique properties, e.g., functionalizability. In this work, a sustainable monomer synthesis is established, and simplified to industrial needs. For the sterically demanding in-bulk ROP to limonene polyamides, various initiators and conditions are tested. Polyamides with more than 100 monomer units are successfully synthesized and confirmed via nuclear magnetic resonance (NMR) spectroscopy and gel permeations chromatography (GPC). Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) are used to analyze its thermal properties. In summary, a sustainable monomer synthesis is established, and promising polyamides with intact double bond and interesting thermal properties are achieved.