Synthesis of alternating polyesters using a dual catalytic system of alkali metal alkoxides and crown ether

Abstract

In this study, a dual catalytic system that merges crown ether with alkali metal alkoxides (AMA) is utilized in the ring-opening alternating polymerization (ROAP) of phthalic anhydride (PA) and propylene oxide (PO). This method streamlines the production of polyesters characterized by a fully alternating sequence, a modifiable molar mass (achieving up to 59.3 kg mol⁻¹), and a narrow molar mass distribution (Ð_M < 1.26). Analysis of various commercially available AMAs, notably sodium ethoxide (EtONa), sodium methoxide, and lithium ethoxide, in tandem with crown ethers (15-crown-5 and 18-crown-6), underscores the superior catalytic efficacy of the EtONa and 18-crown-6 pairing. This heightened efficiency is attributed to the coordination of crown ether with alkali metal ions, thereby boosting the nucleophilicity of terminal alkoxide anions. The methodology has been successfully deployed in the ROAP of PA, norbornene anhydride, and multiple epoxides, while also simplifying the creation of aliphatic–aromatic block polyesters from a mixture of PA, PO, and lactide. This strategy presents a straightforward approach to polyester production, thus making significant contributions to the evolution of polyester synthesis technology.