Columnar Stacks of Star- and Tadpole-Shaped Polyoxazolines Having Triphenylene Moiety and Their Applications for Synthesis of Wire-Assembled Gold Nanoparticles

We report on synthesis, association behavior, and application of six-arm star-shaped and tadpoleshaped amphiphilic polyoxazolines from triphenylene initiators. We synthesized two kinds of novel triphenylene initiators: 2,3,6,7,10,11-hexa(6-bromohexyloxy)triphenylene (initiator for star-shaped polyoxazoline) and 2-(6-bromohexyloxy)-3,6,7,10,11-pentahexyloxytriphenylene (initiator for tadpole-shaped polyoxazoline). Ring-opening cationic polymerization of 2-methyl-2-oxazoline from these initiators successfully produced star- and tadpoleshaped polyoxazolines. Both the star- and tadpole-shaped polyoxazolines formed supramolecular associations in aqueous media due to pi-pi stacking of hydrophobic triphenylene moiety. Critical micelle concentrations (CMCs) and amounts of pi-pi stacking of the star- and tadpole-shaped polyoxazolines in aqueous media were investigated by H-1 NMR and fluorescence measurements. From tapping mode atomic force microscopy (TM-AFM) measurements, the star-shaped polyoxazolines formed straight columnar stacks due to pi-pi stacking of hydrophobic disklike core of triphenylene moiety and symmetric star-shaped structure. In contrast, crooked nanowires were observed in the tadpole-shaped polyoxazoline. Tadpole shape was asymmetric, and thus ordered pi-pi stacking of hydrophobic triphenylene moiety was suppressed. Moreover, by using the columnar stacks of the star-shaped polyoxazoline as a template, we successfully synthesized wire-assembled gold nanoparticles.