Quasi-alternating copolymerization of oxiranes driven by a benign acetate-based catalyst.

Alternating copolymers are distinctly unique in comparison with other copolymers. Herein, an in-depth investigation of the oxyanionic ring-opening copolymerization of propylene oxide (PO) and allyl glycidyl ether (AGE) from benzyl alcohol (BnOH) activated with potassium acetate (KOAc) complexed by 18-crown-6 ether (18C6) is described. We demonstrate that the 18C6/KOAc complex is an efficient and benign catalytic system to promote copolymerization of both oxirane monomers, leading to well-defined polyethers with varied comonomer content and low dispersity values (ƉM < 1.20). Kinetic analysis confirmed the controlled nature of the (co)polymerization process, and the determination of reactivity ratios revealed a quasi-alternating copolymerization profile, according to the Fineman-Ross method. The comparison between the quasi-alternating-type PO/AGE copolymerization and block or gradient copolymerization revealed significant differences, to confirm the different sequence incorporation in the different topological copolymers. These results highlight the great potential of 18C6/KOAc-mediated copolymerization process for the controlled sythesis of a series of copolymer topologies.

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

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 SN 2 process at room temperature and in solvent-free conditions while drastically limiting the occurrence of parasitic hydrogen abstraction 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 (DM < 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.