Ring-Opening Copolymerizations of a CO₂-Derived δ-Valerolactone with ϵ-Caprolactone and l-Lactide

Ring-opening random, gradient, and block copolymerizations of CO₂-derived δ-valerolactone 3-ethyl-6-vinyltetrahydro-2H-pyran-2-one (EtVP) with ϵ-caprolactone (ϵ-CL) and l-lactide (LLA) are reported. By employing both concurrent and sequential addition strategies, we could access a variety of thermal and physical properties. Concurrent copolymerization of EtVP with ϵ-CL yielded gradient copolymers with low glass transition temperatures, while block copolymerizations via sequential addition led to semicrystalline materials regardless of monomer feed ratios. For LLA copolymerizations, glass transition temperatures increased with LLA incorporation regardless of the addition method, but higher T_g values were observed in block copolymerizations from sequential addition. Tensile testing of poly(EtVP-b-LLA) with a molar ratio of 40:60 EtVP:LLA resulted in σ = 0.8 MPa, E = 5.6 MPa, and 83% elongation at break. The chemical recyclability of EtVP-based copolymers was explored as an end-of-life option. Both ϵ-CL and LLA copolymers could be recycled, with block copolymers giving higher yields of recycled monomers than random copolymers.