A facile method to synthesize carboxyl-functionalized magnetic polystyrene nanospheres

Magnetic polystyrene nanospheres with high magnetite content and abundant surface carboxyl groups were prepared by emulsifier-free emulsion polymerization in the presence of aqueous magnetic fluid coated with oleic acid and 10-undecenoic acid as primary and secondary surfactants respectively. The effects of initiator concentration, initiator type (water-soluble or oil-soluble), monomer concentration and ferrofluid content on the particle characteristics such as the size, morphology, magnetic properties and the number of carboxyl groups were investigated. When water-soluble potassium peroxodisulfate (KPS) was used as the initiator, magnetite nanoparticles were uniformly encapsulated in polystyrene particles, while in the oil soluble benzoyl peroxide (BPO) system, magnetite particles were located on one side of magnetic polystyrene nanospheres. The results showed that two mechanisms for the nucleation and growth of nanospheres were involved according to the kind of initiator used in the polymerization. The magnetic nanospheres were superparamagnetic with the highest saturation magnetization of 29.78 emu/g and the corresponding magnetite content of 41.67%. The maximum amount of surface carboxyls was 0.5594 mmol/g. BSA (bovine serum albumin) was used to test the immobilization capacity of proteins onto the magnetic spheres. The immobilization capacity was about 196.2 mg BSA/g. These carboxylated magnetic polystyrene nanospheres have extensive potential biomedical applications.