Magnetic and temperature-sensitive release gels from supramolecular polymers

Abstract

Supramolecular gels consisting of trivalent polyisobutylene and bivalent poly(ethylene oxide) are generated. Strong hydrogen bonding interactions, affixed to the end-group moieties of the respective polymers (binding constant Kassn = 105 M-1), serve as molecular glue, leading to the formation of weak gels. Two different gels were prepared: one, with a short telechelic poly(ethylene glycol) (PEG) segment (gel A), and one with a longer PEG segment (number-average molecular weight Mn = 2000 g mol-1) (gel B). Both gels show a significant increase in viscosity upon mixing of the two polymeric components, with a lag time of several minutes, indicative of nucleation mechanisms as the formation principle. However, only gel A displays classical gel-like behavior, with a loss modulus G′ larger than the storage modulus G″ after formation. Both gels display microphase-separated behavior with a spacing between 4-5 nm as probed via small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) measurements. The incorporation of magnetic nanoparticles (Fe2O 3; radius r=3.5 nm) is successfully achieved, generating new magnetic gels with strongly thermoresponsive properties, displaying a strong temperature-dependent release profile of included dye molecules. Magnetic measurements indicate a superparamagnetic behavior of the incorporated nanoparticles, prospecting the application as magneto-sensitive delivery gels for pharmaceutical purposes. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.