Side-chain modification of π-stacked helical poly(quinoline-2,3-diylmethylene) via thiol-ene reaction

The modification of side-chain substituents is crucial in defining the structure and physical properties of polymers. In this study, we successfully developed a novel method for the versatile modification of side-chain substituents in poly(quinoline-2,3-diylmethylene) (PQM), a polymer characterized by its pi-stacked helical structure. A monomer, featuring a reactive olefin moiety in the side chain of o-allenyl arylisocyanide, was synthesized, and a cyclo-copolymerization reaction was conducted using an organopalladium complex as the initiator. This reaction proceeded selectively, preserving the olefin moieties, and resulted in a pi-stacked helical PQM with olefin moieties uniformly arranged along the helical axis. A thiol-ene reaction with various thiols enabled the introduction of a broad range of substituents into the PQM while maintaining its helical structure. Importantly, the addition of these substituents significantly enhanced the solubility and solvent stability of PQM. Notably, the incorporation of bulky sugar derivatives sustained the helical structure even in polar solvents such as acetonitrile. Additionally, this method facilitated the synthesis of block, random, and grafted copolymers, as well as grafted polymers with poly-lactides, expanding the array of potential applications. The development of this facile method for side-chain modification opens new possibilities for exploring the physical properties and functional applications of pi-stacked PQM.