Chiral random poly(quinoxaline-2,3-diyl) polymers of the sergeants-and-soldiers-type (sergeant units bearing (S)-3-octyloxymethyl groups) adopt an M- or P-helical conformation in the presence of achiral units bearing propoxymethyl or butoxy groups (soldier units), respectively. Unusual bidirectional induction of the helical sense can be observed for a copolymer with butoxy soldier units upon changing the mole fraction of the sergeant units. In the presence of 16-20% of sergeant units, the selective induction of a P-helix was observed, while the selective induction of an M-helix was observed for a mole fraction of sergeant units of more than 60%. This phenomenon could be successfully employed to control the helical chirality of copolymers by applying either random or block copolymerization protocols. Random or block copolymerization of sergeant and soldier monomers in a 18:82 ratio resulted in the formation of 250mers with almost absolute P- or M-helical conformation, respectively (>99% ee). Incorporation of a small amount of coordination sites into the random and block copolymers resulted in chiral macromolecular ligands, which allowed the enantioselective synthesis of both enantiomers in the Pd-catalyzed asymmetric hydrosilylation of β-methylstyrene.

A metal-free initiating system for the living cationic polymerization of alkyl vinyl ethers (VEs) and styrene derivatives was developed using diaryliodonium salts as an organic Lewis acid catalyst. Unlike many past examples of their use as a photoinitiator, diaryliodonium salts were demonstrated to function as a Lewis acid catalyst for cationic polymerization. The cationic polymerization of isobutyl VE smoothly proceeded using a diaryliodonium salt in conjunction with a cationogen that generates a carbon−halogen propagating end, yielding polymers with predictable molecular weights and very narrow molecular weight distributions. The central iodine atom of the diaryliodonium salt most likely exhibited Lewis acidity, thereby generating a dormant−active equilibrium through the reversible generation of a carbocation via the abstraction of the halogen anion from the propagating end. The role of the diaryliodonium salts as Lewis acid catalysts was confirmed by a series of experiments that focused on the effects of concentrations, substituents on the aryl rings, and counteranions. Polymerizations of styrene derivatives and VEs with polar groups also proceeded using diaryliodonium salts in a controlled manner.

Poly(quinoxaline-2,3-diyl) containing (S)-3-octyloxymethyl side chains was synthesized to investigate the induction of a single-handed helical sense to the main chain in various alkane solvents. The polymer showed an efficient solvent dependent helix inversion between n-octane (M-helix) and cyclooctane (P-helix). After a screening of alkane solvents, it was found that linear alkanes having large molecular aspect ratios induced M-helical structure, and branched or cyclic alkanes having small molecular aspect ratios induced P-helical structure. A polymer ligand containing (S)-3-octyloxymethyl side chains and diphenylphosphino pendants also exhibited solvent-dependent helical inversion between n-octane and cyclooctane, leading to the highly enantioselective production of the both enantiomeric product in a palladium-catalyzed asymmetric hydrosilylation reaction of styrene (R-product 94% ee in n-octane and S-product 90% ee in cyclooctane).

Poly(quinoxaline-2,3-diyl)s containing (S)-2-methylbutoxy side chains were found to exhibit blue circularly polarized luminescence (CPL). The handedness of the CPL could be switched by a solvent-dependent helix inversion of the polymer backbone between chloroform (M-helical structure) and 1,1,1-trichloroethane (P-helical structure).