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

摘要

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/TiCl4 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 sigma(-) values, which account for the enhanced resonance effects, were more appropriate for the relationship with the tacticity than the normal sigma 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. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019