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.
Bibliographical noteFunding Information:
The methodology development and kinetic studies were supported by the Young Investigator Program of the Army Research Office (W911NF-19-1-0115). The substrate scope and chirality studies were supported by the National Science Foundation under a CAREER award (CHE-1847362). Funding for the computational modeling portion of this project was provided by the Center for Sustainable Polymers, a National Science Foundation supported Center for Chemical Innovation (CHE-1901635). We thank Prof. Jeff Aubé for expertise regarding in situ IR instrumentation. We also thank Prof. Joseph Templeton, Prof. Kevin Frankowski, and Dr. Andreas Wierschen for thoughtful discussions. We thank the Minnesota Supercomputing Institute (MSI) for providing key computational resources.
© 2020 American Chemical Society.
PubMed: MeSH publication types
- Journal Article
- Research Support, U.S. Gov't, Non-P.H.S.