Ring-opening polymerization (ROP) is a powerful approach to prepare well-defined polymers. Herein, a one-component Lewis pair strategy was adopted, and two delicate Lewis pairs 1–2 were rationally designed and conveniently synthesized. Lewis pairs 1–2 featured an electropositive phosphonium cation, two electrophilic boron centers involving two 9-borabicyclo[3.3.1]­nonane moieties, and a nucleophilic halide (Br– or I–). Lewis pair 1–2-mediated ROP of propylene oxide (PO) exhibited activity (turnover frequency = 3600 h–1) with a living characteristic and low catalyst feeding (0.003 mol %) and afforded an extremely high-molecular-weight α-halide/ω-OH polypropylene oxide (PPO, M n = 489.5 kg/mol) under mild conditions (−30 to 0 °C). We highlight the success of the one-component Lewis pair strategy to achieve living PO polymerization and extremely high-molecular-weight PPO attributing to two important factors: better control (less transfer reaction) and rapid polymerization kinetics, which takes full advantage of the unique structures and the synergistic effect of 1–2. A preliminary investigation demonstrated that water can be added to the polymerization setup and served as a chain transfer reagent, leading to a controlled polymerization and producing α-hydroxy/ω-OH PPO. The present study provides an insightful mechanistic understanding of the designed one-component Lewis pair systems in epoxide homopolymerization based on spectroscopic data analysis and density functional theory calculations.

It is an effective strategy to tailor material properties by copolymerization of monomers with different chemical structures and to adjust the compositions and sequence distributions of resultant copolymers. Although the biorenewable α-methylene-γ-butyrolactone (MBL) as a comonomer has shown potential advantages to impart its copolymers with tunable properties and modifiable pendent vinyl groups, the copolymerization of MBL with other cyclic lactones to exclusively produce functional copolyesters with high MBL content remains as a big challenge mainly owing to the competing polymerization of highly stable five-membered γ-butyrolactone ring and highly reactive exocyclic double bond. In this contribution, we presented the first organocatalytic ring-opening copolymerization (ROCP) of MBL with two cyclic lactones, i.e., ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL), to produce exclusively functional copolyesters without formation of vinyl-addition P(MBL) VAP homopolymer. Copolyesters with MBL content in a wide range from ∼6 to ∼90 mol % were achieved by employing an organophosphazene base/urea binary catalytic system. The obtained copolyesters exhibited composition-dependent thermal properties, which have been carefully investigated herein.

Although significant advances have been achieved, highly stereocontrolled polymerization using organocatalysts is still a great challenge, such as ring-opening polymerization of racemic lactide (rac-LA) for the synthesis of stereoregular polylactide (PLA). In this context, a series of binary organocatalysts consisting of different phosphazenes (CTPB, C3N3-Me-P3, C3N3-Py-P3, t-BuP2, and t-BuP4) and achiral ureas (U1–U6) were applied for the stereocontrolled ROP of rac-LA under mild conditions. It is remarkable that C3N3-Py-P3/U4 with the compatible basicity/acidity showed both high activity (92% conversion within 10 min) and great stereoselectivity (P m = 0.92) at room temperature (20 °C), and the resultant stereoblock PLA had predictable molar mass, narrow distribution (Đ = 1.07), and high melting temperature (T m = 190 °C). Interactions involved among phosphazene, urea, and initiator were investigated by an in situ NMR technique. It was found that C3N3-Py-P3 reacted with benzyl alcohol (BnOH) to form a relatively loose ion pair in the presence of U4, which accounted for both high activity and stereoselectivity. Kinetics studies for different LA monomers at 20 °C showed k obs –1 (rac-LA) = 0.212 min–1, k obs –1 (D-LA) = 0.311 min–1, and k obs –1 (L-LA) = 0.317 min–1, indicative of the chain end control mechanism for stereocontrolled ROP.

Organocatalytic, metal‐free ring‐opening alternating copolymerization (ROAP) of epoxides and cyclic anhydrides to produce polyesters with well‐defined alternating structure remains a challenge despite several organocatalysts having been reported. Herein, the ROAP of cyclohexene oxide (CHO) with phthalic anhydride (PA) using a series of carboxylic acids as initiator in the presence of an organic cyclic trimetric phosphazene base (CTPB) as catalyst is reported. The molar ratio of CTPB to carboxylic acid is proven to be crucial to obtain polyester with well‐defined alternating structure without formation of polyether homopolymer. The effects of carboxylic acid, temperature and feed molar ratio on monomer conversions and resultant molecular weights of poly(PA‐alt‐CHO) are systematically investigated. This work enriches the opinion of initiator for the ROAP of epoxides and cyclic anhydrides.

Polycarbonate/polyester copolymers with high incorporation of EC were realized by a fast and selective process using a metal-free catalyst.