Mechanistic Insight into the Stereoselective Cationic Polymerization of Vinyl Ethers

Abstract

The control of the tacticity of synthetic polymers enables the realization of emergent physical properties from readily available starting materials. While stereodefined polymers derived from nonpolar vinyl monomers can be efficiently prepared using early transition metal catalysts, general methods for the stereoselective polymerization of polar vinyl monomers remain underdeveloped. We recently demonstrated asymmetric ion pairing catalysis as an effective approach to achieve stereoselective cationic polymerization of vinyl ethers. Herein, we provide a deeper understanding of stereoselective ion-pairing polymerization through comprehensive experimental and computational studies. These findings demonstrate the importance of ligand deceleration effects for the identification of reaction conditions that enhance stereoselectivity, which was supported by computational studies that identified the solution-state catalyst structure. An evaluation of monomer substrates with systematic variations in steric parameters and functional group identities established key structure−reactivity relationships for stereoselective homo-and copolymerization. Expansion of the monomer scope to include enantioenriched vinyl ethers enabled the preparation of an isotactic poly(vinyl ether) with the highest stereoselectivity (95.1% ± 0.1 meso diads) reported to date, which occurred when monomer and catalyst stereochemistry were fully matched under a triple diastereocontrol model. The more complete understanding of stereoselective cationic polymerization reported herein offers a foundation for the design of improved catalytic systems and for the translation of isotactic poly(vinyl ether)s to applied areas.

Recent Advances in Living Cationic Polymerization with Emerging Initiation/Controlling Systems

“…Inspired by asymmetric ion‐pair catalysis, the Leibfarth group [ 104,105 ] demonstrated that the combination of Ti‐catalyst and chiral 1,1′‐bi‐2‐naphthol (BINOL)‐based phosphoric acid as a ligand enabled stereoselective polymerization ( Figure A), providing a range of isotactic PVEs with high degrees of isotacticity at −78 °C with several hours of reaction time. The obtained stereocontrolled PVEs exhibit attractive properties.…”

“…Reproduced with permission. [ 104 ] Copyright 2020, American Chemistry Society. B) ɑ,ɑ,ɑ′,ɑ′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol (TADDOL); Reproduced with permission.…”

Designing Weakly Solvating Solid Main-Chain Fluoropolymer Electrolytes: Synergistically Enhancing Stability toward Li Anodes and High-Voltage Cathodes

“…Nuclear magnetic resonance (NMR) was recorded with an Advanced III 400 MHz Bruker spectrometer and an Advanced III 600 MHz spectrometer at 25 °C. 1 H NMR signals were measured relative to the signal for residual chloroform (7.26 ppm) in deuterochloroform (CDCl3), are reported in δ units, parts per million (ppm). 19 F NMR signals are reported in ppm units.…”

“…19 F NMR signals are reported in ppm units. 1 H-19 F NMR signals were reported in ppm units. Sizeexclusion chromatography (SEC) measurements were performed on an Agilent 1100 system equipped with a G1310A pump and a G1362A refractive index detector using THF as the eluant (1.0 mL/min at 35 ºC).…”

“…Other reagents were used without further purification. Diethylene glycol methyl vinyl ether, [1] chain transfer agent (CTA), [2] photo catalyst [3] were synthesized according to literatures. Lithium metal was purchased from China Energy Lithium.…”