Magnetically loaded poly(methyl methacrylate-co-acrylic acid) nano-particles

Magnetically loaded polymeric nano-particles carrying functional groups on their surface were prepared by a two-stage process. In the first stage, super-paramagnetic magnetite (Fe₃O₄) nano-particles were produced by a co-precipitation method from the aqueous solutions of FeCl₂·4H₂O and FeCl₃·6H₂O using a NaOH solution. The smallest size obtained was 40.9 nm with poly-dispersity index of 0.194 obtained by using a Zeta Sizer. The effects of Fe²⁺/Fe³⁺ molar ratio, stirring rate, temperature, base concentration, and pH on the particle size/size distribution and stability of the dispersions were examined. Increasing the relative concentration of Fe²⁺ ion and decreasing the stirring rate and pH increased the particle size, while the concentration of NaOH and temperature did not change the particle size significantly. Polymer coating was achieved by emulsion polymerization at high surfactant to monomer ratio of methyl methacrylate (MMA) and acrylic acid which were used as comonomers (comonomer ratio: 90/10 weight) with high surfactant to monomer ratio. The surfactant and initiator were SDS and KPS, respectively. Nano-particles in the range of 115 and 300 nm in diameter were produced depending on recipe. Increasing the Fe₃O₄/monomer and surfactant/monomer ratios, the KPS concentration caused a decrease in the average diameter. Magnetic properties of the nano-particles were obtained by electron spin resonance and vibrating-sample magnetometer. Most of the polymer-coated nano-particles exhibited super paramagnetic behavior.