Methylmethacrylate sulfopropylmethacrylate copolymer nanoparticles for drug delivery .1. Preparation and physicochemical characterization

Methylmethacrylate (MMA) sulfopropylmethacrylate (SPM) copolymer nanoparticles were prepared by free radical polymerization. The conditions of preparation were varied with regard to the concentration of initiator and monomer, and copolymer composition. Nanoparticles with a yield greater than 80% were produced. The particles were characterized in terms of particle size, size distribution, particle charge (zetapotential) and molecular weight. The data were compared to pure polymethylmethacrylate (PMMA) nanoparticles. The copolymer composition was shown to influence particle size and particle charge. The influence of the total monomer amount in the polymerization medium on the particle size was characteristic up to a concentration of 2% depending on the solubility of MMA in water at the temperature of reaction. An increasing amount of total monomer led to particle sizes of 60-130 nm for low monomer concentrations (0.5%), depending on the proportion of SPM (0-10%), to 120-280 nm for higher total monomer concentrations (greater than 2%). Surface charge as well as particle size were influenced mainly by the proportion of the comonomer SPM in the copolymer. The negative surface charge increased from -52 mV for pure PMMA nanoparticles to -80 mV for the copolymer particles with an SPM content of 10%. In the same range of 0-10% SPM of the total monomer, the particle sizes decreased from 187 to 100 nm. The concentration of the initiator up to a concentration of 0.3% showed no effect on the particle size of the resulting nanoparticle suspension. Higher concentrations led to intolerably large variability in the polymerization process.