Controlled Oxyanionic Polymerization of Propylene Oxide: Unlocking the Molecular‐Weight Limitation by a Soft Nucleophilic Catalysis

• Published in: Macromolecular rapid communications. 2022-10, Vol.43 (20), p.e2200424-n/a
• Main Authors: Fornaciari, Charlotte, Pasini, Dario, Coulembier, Olivier
• Format: Article
• Language: English
• Subjects: Acetic acid; Alcohols; Carboxylates; Catalysis; crown ethers; multiblock copolymers; Nucleophiles; oxyanionic polymerization; Polymerization; Potassium; Potassium acetate; Propylene oxide; Ring opening polymerization; Room temperature
• ISSN: 1022-1336; 1521-3927
• DOI: 10.1002/marc.202200424

The oxyanionic ring‐opening polymerization of propylene oxide (PO) from an exogenous alcohol activated with benign (complexed) metal‐alkali carboxylates is described. The equimolar mixture of potassium acetate (KOAc) and 18‐crown‐6 ether (18C6) is demonstrated to be the complex of choice for preparing poly(propylene oxide) (PPO) in a controlled manner. In the presence of 18C6/KOAc, hydrogen‐bonded alcohols act as soft nucleophiles promoting the PO SN2 process at room temperature and in solvent‐free conditions while drastically limiting the occurrence of parasitic hydrogen ion generally observed during the anionic ROP of PO. The resulting PPO displays predictable and unprecedented molar masses (up to 20 kg mol−1) with low dispersities (ĐM < 1.1), rendering the 18C6/KOAc complex the most performing activator for the oxyanionic polymerization of PO reported to date. Preliminary studies on the preparation of block and statistical copolyethers are also reported. Well‐defined poly(propylene oxide) (PPO), as well as PPO‐based copolymers, are achieved by combining potassium acetate and 18‐crown‐6 ether with alcohols as initiator. The combination of high catalytic efficiency with mild nucleophilicity of the complex allows access to PPO with molar mass as high as 20 kg mol−1 and narrow dispersity (ĐMM < 1.1), owing to the containment of detrimental transfer reactions.