Rheological properties of redox-responsive, associative ferrocene-modified branched poly(ethylene imine) and its modulation by beta-cyclodextrin and hydrogen peroxide

Redox-responsive, hydrophobically associating polymers which can change their structures, conformations and properties through specific redox reaction are interesting, because they can be used to construct novel biosensors and can be applied to environmentally benign electro-functional systems, such as electrically switchable drug delivery systems and sol-gel materials. Studies on the rheological properties of these polymers are essential to realize their applications in these areas. Herein, rheological properties of redox-responsive ferrocene modified branched poly(ethylene imine) (BPEI-Fc) in aqueous solution were studied. The association behavior of this polymer during heating-cooling cycles and with the addition of NaCl was also explored. Viscometric measurements suggest the viscosity of this system can be markedly reduced by the introduction of beta-cyclodextrin. H-1 NMR results indicate inclusion compounds are formed between b-cyclodextrin and ferrocene. Moreover, hydrogen peroxide can be an alternative way to reduce the viscosity of BPEI-Fc solution as demonstrated by viscometric measurements and UV/Vis spectroscopy. With these outstanding properties, we expect this system may find wide applications in biosensors, drug delivery and electrically switchable materials.