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

The challenging ring-opening homo-polymerization of α-ethylidene-δ-vinyl-δ-valerolactone (EVL), de-rived from CO2 and 1,3-butadiene, has aroused ex-tensive attention in consideration of economic effi-ciency and functionalization potential. Here, we achieve the first cationic ring-opening polymeriza-tion (CROP) of EVL, yielding well-defined polyester PEVL with number average molecular weight up to 12.8 kg/mol and low dispersity of 1.2. The obtained PEVL contains two kinds of structural units derived from EVL and three kinds of alkenyl groups, indicat-ing an isomerization during propagation. The isom-erization is necessary to the propagation, evidenced by density functional theory (DFT) calculation and unavailable CROP of the semi-hydrogenated EVL de-rivative without δ-vinyl group (α-ethylidene-δ-ethyl-δ-valerolactone). The fast intramolecular transfer reaction and slow initiation result in the cyclic to-pology fidelity of PEVL, providing the first example of quantitative formation of cyclic polyester in CROP. PEVL is degradable and recyclable, possessing a low glass transition temperature (Tg) of -33.6 ℃, while the product after modification with 1-octadecanethiol exhibits a melting point (Tm) of 42.2 ℃.