Carbenium-Based Cationic Ring-Opening Polymerization of CO₂-Based Disubstituted δ-Valerolactone

The challenging ring-opening homopolymerization of α-ethylidene-δ-vinyl-δ-valerolactone (EVL), derived from CO₂ and 1,3-butadiene, has aroused extensive attention in consideration of economic efficiency and functionalization potential. In the contribution, we achieve the first cationic ring-opening polymerization (CROP) of EVL through a carbenium-based mechanism, yielding well-defined cyclic polyester PEVL with a number-average molecular weight (M_n) up to 12.8 kg/mol and a low dispersity of 1.2. The carbenium-based CROP results in PEVL containing two kinds of structural units derived from EVL, evidenced by NMR, MALDI-ToF MS, and density functional theory (DFT) calculation. The fast intramolecular transfer reaction and slow initiation are responsible for the cyclic topology fidelity of PEVL. The M_n of PEVL is tunable from 6.5 to 12.8 kg/mol by decreasing the polymerization temperature from 10 to -30 °C. PEVL possessing a low glass transition temperature (T_g) of -33.6 °C is ready for postpolymerization functionalization, as showcased by modification with 1-octadecanethiol, which endows the polymer with a melting point (T_m) of 42.2 °C.