Pyridine Isomer Effects in the Framework of Phase-Separated Vitrimer-Like Materials Operated with Trans-N-Alkylation Bond Exchange of Quaternized Pyridines

Abstract

Pyridine groups are known to form various types of bonds, including hydrogen, ionic, and coordination bonds. Another distinctive feature of pyridine groups is the presence of structural isomers. The effects of pyridine isomers have been investigated, particularly for ortho- and para-substituted pyridines, in relation to their bond formation abilities and interaction energies, which ultimately influence macroscopic physical properties. In this study, the effects of pyridine isomers on the formation of quaternization bonds are newly explored, based on the original design of vitrimer-like materials. The polymer component is a poly(acrylate) random copolymer containing ortho-, meta-, and para-substituted pyridine side groups, which are cross-linked by diiodo molecules through pyridine quaternization bonds. The quaternized pyridines self-aggregate into nano-domains, and bond exchange occurs via trans-N-alkylation in an inter-domain manner. The differences in bond formation and related physical properties of samples with three distinct pyridine isomers, including creep and stress relaxation behaviors of the vitrimer-like materials are investigated. Overall, this study offers new insights into the pyridine isomer effects and provides a fresh perspective for tuning the physical properties of bond-exchangeable materials.