Polyester Platform with High Refractive Indices and Closed-Loop Recyclability from CO₂, 1,3-Butadiene, and Thiols

α-Ethylidene-δ-vinyl-δ-valerolactone (EVL) is the only intermediate to synthesize copolymers of CO₂ with 1,3-butadiene whose ring-opening polymerization (ROP), however, is obstructed by the tiglate group. In the contribution, EVL derivatives are synthesized through a Michael addition reaction to saturate the conjugated double bond as well as introduce various groups to synthesize polyesters with designable molecular weights (M_n = 6.9-12.8 kg·mol^-1), narrow dispersities (Đ = 1.08-1.19), tunable glass-transition temperatures (T_g = -45-3 °C), and excellent refractive indices (n_d = 1.64-1.79) via living and controlled ROP. The obtained polyesters are able to be recycled to the corresponding monomers, which can prepare comparable polymers with identical side groups, realizing the homorecycling. In addition, the retro-Michael addition reaction is established and employed, realizing heterorecycling, which can alter properties during recycling. We propose a strategy for EVL derivatives and establish the corresponding polyester platform with not only high refractive indices and tunable T_gs, but also the ability to tailor properties during recycling.