Autonomous viscosity oscillation viametallo-supramolecular terpyridine chemistry of branched poly(ethylene glycol) driven by the Belousov-Zhabotinsky reaction

Herein, we report an autonomous viscosity oscillation of polymer solutions coupled with the metal-ligand association/dissociation between Ru and terpyridine (tpy), driven by the Belousov-Zhabotinsky (BZ) reaction. The tpy ligand for the Ru catalyst was attached to the terminals of poly(ethylene glyc...

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Veröffentlicht in:Soft matter 2014-02, Vol.10 (9), p.1349-1355
Hauptverfasser: Ueki, Takeshi, Takasaki, Yumi, Bundo, Kaori, Ueno, Tomonaga, Sakai, Takamasa, Akagi, Yuki, Yoshida, Ryo
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Sprache:eng
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Zusammenfassung:Herein, we report an autonomous viscosity oscillation of polymer solutions coupled with the metal-ligand association/dissociation between Ru and terpyridine (tpy), driven by the Belousov-Zhabotinsky (BZ) reaction. The tpy ligand for the Ru catalyst was attached to the terminals of poly(ethylene glycol) (PEG) with different numbers of branches (linear-, tetra-, and octa-PEG). It is well known that mono-tpy coordination is stable when Ru is oxidized (Ru(tpy) super(3+)), whereas bis-tpy coordination is stable when the Ru centre is reduced (Ru(tpy) sub(2) super(2+)). In the oxidized state, the three different polymers existed as solutions. In contrast, when the Ru centre was reduced, gels were obtained for the tetra- and octa-PEG owing to the formation of a three-dimensional polymer network through Ru-tpy coordination. Rheological measurements confirmed that the sol-gel transition occurred much more quickly in the octa-PEG system than in the tetra-PEG system, because of the requirement of fewer crosslinking points. The polymer solutions exhibited self-oscillation of absorbance and viscosity when BZ substrates were added to the solutions of Ru super(2+)-tpy-modified tetra-/octa-PEG. This indicated that the Ru(tpy) sub(2) super(2+) attached to the polymer ends could work as a metal catalyst for the BZ reaction. By increasing the number of branches from 4 to 8, the amount of crosslinking changed more remarkably during the oscillation, with a maximum value closer to that necessary for gelation. Thus, viscosity oscillation with a larger amplitude in the region of higher viscosity was achieved by using octa-PEG.
ISSN:1744-683X
1744-6848
DOI:10.1039/c3sm51537k