Synthesis of Bifunctional Copolyesters via Chemoselective Ring-Opening Copolymerization of δ-Lactone Derived from CO₂ and Butadiene with ε-Caprolactone

3-Ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVP), derived from the telomerization of carbon dioxide (CO2) with 1,3-butadiene, emerges as a promising intermediate for the production of high-value added materials from CO2. However, the current impediment lies in the challenge of accessing selective ring-opening (co)polymerization of EVP because of unfavorable thermodynamics under mild conditions and the competitive polymerization of highly reactive C═C double bonds. In this study, we report the chemoselective ring-opening copolymerization of EVP (selective ring-opening rather than vinyl polymerization) with ε-caprolactone (CL), even at room temperature, by using a phosphazene/urea binary catalyst. This process exclusively yields the ring-opening product of copolyester poly(CL-co-EVP). The resultant poly(CL-co-EVP)s exhibit predictable molar masses (Mns), narrow distributions (D̵ < 1.2 for most cases), wide range of EVP-contents (0–60 mol %), and thus tunable thermal properties. The kinetic and reactivity ratio (rCL = 3.67 and rEVP = 0.17) studies indicate a gradient structure for poly(CL-co-EVP). Moreover, these poly(CL-co-EVP)s possess two distinct pendant alkene groups, an internal one and a terminal one, which are ready to undergo sequential functionalization to prepare bifunctional polyesters or form cross-linked polyesters. Poly(CL-co-EVP) copolyester with only a 2 mol % EVP incorporation shows a significant improvement in both tensile strength (σb) and elongation at break (εb) in comparison to PCL homopolymer with a similar Mn, while cross-linking further facilitates the transformation of PCL from thermoplastics to elastomers. This study opens avenues to utilize EVP and synthesize sustainable and functional polyesters.