Thermoresponsive Dendronized Poly(phenylacetylene)s via Dynamic Covalent Chemistry Showing Multiple-Responsive Chirality

Helical polymers with dynamic chirality are interesting not only for understanding the relationship between polymer structure and chiral conformation but also for developing responsive chiral polymeric materials. We report here the synthesis and characterization of a homologous series of dendronized poly-(phenylacetylene)-s (PPAs) via both macromonomer and grafting-to routes. These copolymers consist of achiral units carrying dendritic oligoethylene glycol (OEG) pendants and chiral units of dynamic imines formed from aldehydes and amino acids, which combine the constitutional dynamic chemistry (Schiff base) in the pendants with the conformational dynamic PPA backbones. Dendritic OEG pendants endow these copolymers with characteristic thermoresponsive behavior. The principles for modulating the helicity of these dendronized copolymers were examined, and factors including molecular structures (copolymer compositions and pendant linkage via ester or amide), solution pH, and thermally induced phase transitions have been investigated. These copolymers adopt tailored helicities in the presence of additional amino acids through multiple interaction balances between the copolymers and the amino acids. We believe that the methodology developed in this work will pave a convenient way to afford optically inactive copolymers or active polymers with featured dynamic helicity.