Polymer stabilized magnetite nanoparticles and poly(propylene oxide) modified styrene-dimethacrylate networks

Magnetic nanoparticles that display high saturation magnetization and high magnetic susceptibility are of great interest for medical applications. Nanomagnetite is particularly desirable because it displays strong ferrimagnetic behavior, and is less sensitive to oxidation than magnetic transition metals such as cobalt, iron, and nickel. For in-vivo applications, it is important that well-defined organic coatings surround the nanomagnetite particles. It is rationalized that this will prevent any aggregation of the nanoparticles in-vivo, and may also enable efficient excretion and protection of the body from toxicity.; Magnetite nanoparticles can be prepared by co-precipitating iron (II) and iron (III) chloride salts in the presence of ammonium hydroxide at pH 9–10. Oleic acid is known to effectively stabilize dispersions of nanomagnetite in nonpolar solvent. Stabilization occurs because the carboxylic acid group covalently reacts with the surface of the magnetite and the aliphatic chain extends out into the nonpolar solvent, preventing aggregation of the particles by a steric (entropic) mechanism. One goal of this work has been to develop a generalized methodology for stabilizing nanomagnetite dispersions using well-defined, non-toxic, block copolymers, so that the resultant magnetite-polymer complexes can be used in a range of biomedical materials. My objectives have included: (1) Understanding what types of polymer structures bind irreversibly to magnetite at the physiological pH and what block lengths are desirable, (2) Tailoring polymer block lengths to maximize the concentration of bound magnetite, yet preserve good dispersion and (3) Designing copolymers with both hydrophilic and hydrophobic tail blocks to enable dispersion in different types of carrier fluids.; Hydrophilic triblock copolymers with controlled concentrations of pendent carboxylic acids were designed as steric stabilizers for magnetite nanoparticles. The triblock copolymers contain carboxylic acids in the central anchor block and controlled molecular weight poly(ethylene oxide) tail blocks. They were utilized to prepare hydrophilic-coated iron oxide nanoparticles with biocompatible materials for magnetic field guidable drug delivery vehicles. The triblock copolymers synthesized contain 3, 5, or 10 carboxylic acids in the central segments with M_n values of 2000, 5000 or 15000 g/mol poly(ethylene oxide) tail blocks. A method was developed for preparing ≈10 rim diameter magnetite surfaces stabilized with the triblock polymers. The carboxylic acid is proposed to covalently bind to the surface of the magnetite and form stable dispersions at neutral pH. Stable dispersions were prepared with all triblock copolymers investigated. The polymer-nanomagnetite conjugates described in this thesis have a maximum of 35 wt. % magnetite and the nano-magnetite particles have an excellent saturation magnetization of ∼66–78 emu/g Fe ₃O₄. Magnetization curves show minimal hysteresis. Powder X-ray diffraction (XRD) confirms the magnetite crystal structure, which appears to be approximately single crystalline structures via electron diffraction spectroscopy analysis (EDS). These materials form stable magnetic dispersions in both water and organic solvents. Transmission electron microscopy (TEM) photomicrographs show that the dispersions contain 10 nm diameter magnetite coated with the polymeric coatings.