Poly(ferrocenylsilane) Polyelectrolyte Hydrogels with Redox Controlled Swelling
Stimulus-responsive hydrogels1 are attracting much attention due to their potential use in controlled release systems2 where drugs or cosmetics can be released upon receiving a specific stimulus, or as actuators, artificial muscles or valves.3,4 Typical stimuli used to date include temperature, pH, ionic strength, light and to a much lesser extent redox stimuli.5 Redox stimuli may offer fast and reversible switching between states and can be applied externally. In addition, due to access to nanofabricated electrodes or metallic lines, redox-responsive systems can be addressed at the nanoscale.
In this project we aim to form redox-responsive poly(ferrocenylsilane) (PFS)6 polyion hydrogels based on water-soluble PFS polyelectrolyte chains.7 PFS chains are composed of alternating ferrocene and silane units and can be reversibly oxidized and reduced by chemical and electrochemical means.8 PFS hydrogels may undergo redox-induced volume changes or changes in viscoelastic properties due to alterations in chain conformation, charge density and polarity of the constituent polymer chains.9
PFS polycation hydrogel
PFS polyanion hydrogel
Figure 1:Examples of synthesis and crosslinking reactions of PFS polyions to form organometallic hydrogels.
The project involves synthesizing PFS chains with suitable reactive side groups for introducing ionic and crosslinkable functional groups. In the case of the polycation, crosslinking will be achieved using di- or triamines but for the polyanion network a new crosslinking route will be tried using thiol-ene10 or related double-bond addition reactions such as hydrosilylation.
The redox-responsive behavior of the hydrogels will then be studied. Initial work has shown that the polyanion network collapses upon oxidation, because the positive charges generated in the PFS main chain are compensated by the negatively charged sulfonate side groups. The resulting charge-compensated network is much less compatible with water and collapses.
Upon reduction, the network returns to its initial polyanion state and swells again in water. Therefore, the polyanion hydrogel seems to be of potential use as actuator or as a system for controlled release of encapsulated molecules.
Figure 2:PFS Polyanion Hydrogel 5.
Work in this project includes polymer synthesis and characterization by 1H NMR and Gel Permeation Chromatography. As some steps require working under dry conditions, the student will gain expertise in working with (high) vacuum lines, under inert atmosphere or in a glove box. Electrochemical oxidation and reduction will be carried out using cyclic voltammetry. The mechanical response of the hydrogels to redox stimuli will be studied by means of a rheometer or by dynamic mechanical analysis.
Phone: +31 53 4892975
1. For a review on Hydrogels see: Polymer Gels, Fundamentals and Applications, Bohidar, H. B.; Dubin, P.; Osada, Y., Eds.; American Chemical Society: Washington DC, 2002; ACS Symposium Series 833.
2. (a) Franssen, O.; Vandervennet, L.; Roders, P.; Hennink, W. E. J. Contr. Release 1999, 60, 211-221. (b) Thornton, P. D.; Mart, R. J.; Webb, S. J.; Ulijn, R. V. Soft Matter 2008, 4, 821-827.
3. Zhang, Y.; Kato, S.; Anazawa, T. Smart Mater. Struct. 2007, 16, 2175-2182.
4. Liu, Z.; Calvert, P. Adv. Mater. 2000, 12, 288-291.
5. (a) Okabe, S.; Sugihara, S.; Aoshima, S.; Shibayama, M. Macromolecules 2003, 36, 4099-4106. (b) Zhang, K.; Huang, H.; Yang, G.; Shaw, J.; Yip, C.; Wu, X. Y. Biomacromolecules 2004, 5, 1248-1255.
6. For reviews on poly(ferrocenylsilanes) see: (a) Manners, I. Macromol. Symp. 2003, 196, 57-62. (b) Kulbaba, K.; Manners, I. Macromol. Rapid Commun. 2001, 22, 711-724. (c) Manners, I. Chem. Commun. 1999, 857-865. (d) Whittell, G. R.; Manners, I. Adv. Mater. 2007, 19, 3439-3468.
7. (a) Power-Billard, K. N.; Manners, I. Macromolecules 2000, 33, 26-31. (b) Hempenius, M. A.; Robins, N. S.; Lammertink, R. G. H.; Vancso, G. J. Macromol. Rapid Commun. 2001, 22, 30-33. (c) Hempenius, M. A.; Vancso, G. J. Macromolecules 2002, 35, 2445-2447. (d) Wang, Z.; Lough, A.; Manners, I. Macromolecules 2002, 35, 7669-7677.
8. (a) Rulkens, R.; Lough, A. J.; Manners, I.; Lovelace, S. R.; Grant, C.; Geiger, W. E. J. Am. Chem. Soc. 1996, 118, 12683-12695; (b) Péter, M.; Lammertink, R. G. H.; Hempenius, M. A.; Vancso, G. J. Langmuir 2005, 21, 5115-5123.
9. Fleischhaker, F.; Arsenault, A. C.; Wang, Z.; Kitaev, V.; Peiris, F. C.; von Freymann, G.; Manners, I.; Zentel, R.; Ozin, G. A. Adv. Mater. 2005, 17, 2455-2458.
10. Hoyle, C. E.; Lee, T. Y.; Roper, T.; J. Polym. Sci. Part A: Polym. Chem. 2004, 42, 5301-5338.