Structure–property relationship of phenoxyimine ligands/metal chloride initiating systems for controlled cationic polymerizations of alkyl vinyl ethers

Abstract

The catalyst structure-property relationships of the phenoxyimine complexes in controlled cationic polymerization of vinyl ethers were investigated based on the Hammett correlation. The correlation analyses of a series of experiments using the phenoxyimine ligands/TiCl 4 initiating systems indicated that the substituents on the N-aryl phenoxyimine ligands affected the polymerization rate and stereoselectivity. Importantly, a linear correlation was observed between the Hammett substituent constants and the polymerization rates, which indicates that the Lewis acidity of the complex is affected by the electron-withdrawing and -donating effects of the substituents. The tacticity of product polymers correlated to the Hammett substituent constants. Unlike the relationship with the polymerization rates, the σvalues, which account for the enhanced resonance effects, were more appropriate for the relationship with the tacticity than the normal σ values. In contrast, the polymerization behavior using o-substituted ligands exhibited a trend different from those using p-or m-substituted ligands. The structural change, which was caused by the rotation of the C N bonding, most likely triggered the acceleration effect in the case of the o-substituents.Additional supporting information may be found in the online version of this article.

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

“…In 2019, the Aoshima group [ 55 ] investigated effect of ligands (salen and salphen ligands) on the metal‐complexes catalyzed LCP via a mechanism similar to their previous work. While good to moderate control over dispersity was obtained for PIBVE, meso dyad values were kept in a range of 60–66%, when either salen or salphen was employed.…”

“…For example, external stimuli (e.g., photon and electron) have been exploited to offer temporal control and sequence regulation; [ 48,51,52 ] organic catalysts have been employed to facilitate propagation without metal‐contamination concern; [ 53 ] chiral ligands have revived the usage of Lewis acid/base pairs, and endowed the capability of tuning the tacticity of polymers. [ 54,55 ]…”