Copolymerizations of a CO₂/Butadiene Derived Six-Membered Lactone with ε-Caprolactone

With the increasing demand for sustainable polymers, monomers sourced solely from renewable resources are in high demand. Hydrogenated δ-lactone (HL), synthesized from CO₂, 1,3-butadiene, and H₂, is a promising candidate. However, its copolymerization behavior remained unexplored, leaving questions about its compatibility with other lactones and its role in copolymer systems. In this study, the copolymerization of HL with various lactones, including glycolide (GA), L-lactide (L-LA), and ε-caprolactone (CL), was systematically investigated. Copolymerizations were carried out under different conditions, and the resulting polyesters were characterized by ¹H NMR, ¹³C NMR, DOSY NMR, GPC, DSC, and TGA. CL was identified as the optimal comonomer for HL, with which it could copolymerize effectively at room temperature. Three chain segment arrangements of poly(HL-co-CL), namely random copolyester (poly(HL-r-CL)), A-B block copolyester (poly(HL-b-CL)), and A-B-A block copolyester (poly(CL-b-HL-b-CL)), were successfully obtained. The thermal stability, glass transition temperature, melting temperature, and mechanical properties of the copolyester can be effectively modulated by adjusting the proportion of CL and HL monomers. Poly(HL₈-b-CL) has a tensile elongation of 568% and a tensile strength of 8.0 MPa. These results suggest that HL is an interesting and attractive renewable monomer for the development of new sustainable polyester materials.