(725f) Transverse Relaxivities of Polyether-Magnetite Complexes: The Effect of Polymer Loading and Composition

Magnetite nanoparticles have many uses, in particular as T2 contrast agents for magnetic resonance imaging (MRI) and for incorporation into magnetic ferrofluids.[1,2] Magnetite particles have relatively low cytotoxicities, and their surfaces are amenable to the adsorption of biocompatible macromolecules.[3] Thus, specific functionalities can be attached to magnetite nanoparticles in order to optimize a specific property for appropriate applications.[4] This study concerns the transverse relaxivities of polyether-magnetite complexes in which both the magnetite and the polyethers were well-defined. The magnetite was synthesized using a method adapted from Pinna et al.[5], which consists of the high temperature decomposition of iron acetylacetonate at high temperature in benzyl alcohol, resulting in well-defined magnetite nanoparticles. Well-defined polyethers with tri-phosphonate anchor groups were synthesized including poly(ethylene oxide) (PEO) homopolymers and amphiphilic poly(propylene oxide)-b-poly(ethylene oxide) (PPO-b-PEO) block copolymers. The triphosphonate end groups provide robust anchoring of the polyether chains on magnetite in phosphate buffered saline.[6] The number average size of dispersed complexes and the half-life for doublet formation of well-defined polyether-magnetite complexes like those in the present study can be predicted with a model based on a star polymer.[4] In the present study, we report transverse relaxivities of the polyether-magnetite complexes that were measured while varying polymer loading, polymer type, and, in the case of the block copolymers, polymer composition.

1. Huffstetler, P. P, et al. Polymer Preprint, 2008, 49(2), 1103-1104. 2. Mefford, et al. Chemistry of Materials, 2008, 20(6), 2184-2191. 3. Harris, L., et al. Chemistry of Materials 2003, 15(6), 1367-1377. 4. Miles, W.C., et al. Langmuir 2009, 25(2), 803-813. 5. Pinna, N., et al. Chemistry of Materials 2005, 17, 3044-3049. 6. Goff, J.D., et al. Chemistry of Materials 2009, 21, 4784?4795.