γ-Methylene-γ-butyrolactone (MBL) is a versatile and chemically reactive five-membered ring lactone monomer that is currently being actively researched as a promising sustainable alternative to conventional petroleum-based plastics, largely due to its inherent potential for efficient chemical recycling back to its monomeric state, particularly through its use as a precursor in the creation of advanced materials like polythioesters and other types of chemically recyclable polyesters.