Kijung Kim

Molecular weight control of PS spheres using soap free and RITP-soap free emulsion polymerization

AbstractThe reversible iodine transfer polymerization (RITP) of styrene in the absence of light was carried out using potassium persulfate (KPS) under argon atmosphere at 80 °C for 7 h and the properties of the polymers were compared to those obtained from the soap-free emulsion polymerization (SFEP). The variables were the concentration of KPS and iodine, molar ratios between KPS and iodine, reaction temperatures, and monomer contents. The results showed that the conversion retarded and reached from 99.5% to 82%, the particle size dramatically increased from 0.335 to 1.37 μm, the molecular weight decreased from 183,000 to 66,000 g/mol, and the polydispersity index (PDI) increased from 2.7 to 3.8 for the presence of 2 wt% of KPS and iodine content between 0 and 0.228 mmol, respectively, implying that the molecular weight was controlled and that the particle stability was reduced with iodine as usual. For the effects of the solid content on particle properties, the monomer conversion and the particle size increased, but the molecular weight and PDI decreased with the increased KPS content and [KPS]/[I2] ratio. The highest content was 30 wt% and this was less than that in the presence of sodium dodecyl sulfate (SDS) in the RITP-emulsion and in the absence of SDS in the SFEP. Thus, the use of an emulsifier in the RITP or SFEP was one of the important factors for obtaining the maximum solid content needed for industrial applications.n

Effect of hydrogen peroxide on the UCST behavior of PMMA in the modified dispersion polymerization

AbstractThe effect of hydrogen peroxide on the formation of molecular weight of poly(methyl methacrylate) (PMMA) in the modified dispersion polymerization using a co-solvent of methanol/water and methanol/hydrogen peroxide aqueous solution was studied. The variables included the molecular weight upon the concentration of initiator and hydrogen peroxide, solubility upon molecular weight and temperature, particle size upon cooling rate, and reversible temperature responsive behavior upon thermal history. The relationship between the temperature and PMMA particle size showed reversible temperature-responsive behavior upon the heating and cooling processes. As a result, hydrogen peroxide was confirmed to act as a co-initiator in reducing the molecular weight of PMMA, a good co-solvent with methanol by improving the solubility and inducing the upper critical solution temperature behavior, and a stabilizer in forming stable particles upon cooling.n

Particle size-dependent magnetic properties of poly (methyl methacrylate) core/nickel shell hybrid spheres

The particle size-dependent magnetic properties of the core/shell type of the poly (methyl methacrylate) (PMMA)/Ni hybrid microspheres were investigated. The electroless nickel plating was carried out by controlling optimum conditions in terms of the initial pH, plating temperature, amount of the nickel plating solution on the Ni content and coating thickness. The thickness of the Ni shell varied from 70 to 225xa0nm from the PSS (Particle Size Systems) measurement and from 73 to 285xa0nm from the theoretical calculation depending on the core sizes. Although the Ni thickness varied upon the core size, the coated total Ni content was approximately 32xa0% and this was independent of the core sizes due to the same concentration of nickel plating solution. In addition, the magnetic moment and the coercivity of PMMA/Ni hybrid particles were 0.14xa0emuu2009·u2009g−1 and 0.12xa0kOe, respectively, which are independent of the particle sizes. Thus, the magnetic moment and coercivity of PMMA core/nickel shell hybrid particles are not influenced by the particle size or the nickel shell thickness, but affected by the total contents of nickel.