A simple and highly active catalytic process for ring-opening alternating copolymerization (ROAC) of cyclic anhydrides and epoxides still remains a key challenge. Herein, we have described an effective group of versatile and low-toxic zinc dicarbyl/amine Lewis pairs for the ROAC. The facile route showed a high catalytic activity (TOF ≤ 210 h⁻¹ at 110 °C) and perfectly alternating selectivity (>99%). An unexpected highly regioselective ring-opening of asymmetric epoxides (PO, ECH and SO) was also achieved by the combination of zinc alkyls (or aryls) and amines. Of note, deprotonation side reaction of α-H of anhydrides with organic bases was uncovered, and subsequently was inhibited by using nonpolar solvents and Lewis acid/base pairs. Thus, an array of polyesters was synthesized by the coupling of various anhydrides (PA, CHA, SA and NA) and epoxides (CHO, PO, ECH and SO) using the same Lewis pairs. Furthermore, variable temperature ¹H NMR spectral and MALDI TOF MS analyses were performed to understand the possible mechanism and microstructure. The experimental results indicated that zwitterionic alkoxide and carboxylate intermediates alternately formed to enhance the ester repeat units in chain initiation and propagation. This work provides a simple and green catalytic strategy to prepare diversified polyesters from the ROAC process of cyclic anhydrides and epoxides with considerable catalytic activity and alternating selectivity.

A metal-free, highly regioselective and stereoregular ring-opening alternating copolymerization (ROAC) of monosubstituted epoxides with tricyclic anhydrides remains a challenge in the advancement of polyester synthesis. Herein, we described an effective group of organic dual catalysts for the ROAC, exhibiting a high catalytic activity (the highest TOF = 330 h⁻¹ at 110 °C), narrow polydispersity (PDI < 1.20) and excellent alternating selectivity (ester > 99%) in a controlled manner. The ROAC of a variety of monosubstituted epoxides and tricyclic anhydrides was carried out under mild conditions. Of importance is the fact that highly regioselective insertion of epoxides has been realized by simple and metal-free catalysts in the ROAC, where the highest regioselectivity is up to 98% for aliphatic epoxides and glycidyl ethers at 80 °C. Styrene oxide bearing electron-withdrawing phenyl also showed a good regioselectivity of 78%. Besides, the complete suppression of epimerization and transesterification was achieved even at high conversion for a variety of tricyclic anhydrides. Furthermore, block and gradient copolymers were synthesized by the sequential addition strategy and one-pot terpolymerization. Accordingly, a green, regioselective and stereoregular fabrication of functional polyesters was realized for the first time by a metal-free process.

Despite the development of new catalysts and synthetic strategies to prepare polyolefin elastomers (POEs), less progress has been made in balancing their elastomeric properties with processability and resistance to heat and solvents.