No abstract

No abstract

SYNOPSISThe influences of polymerization temperature, initiator and monomer concentrations, ionic strength of the aqueous phase, as well as ethylene glycol dimethacrylate (EGDM) comonomer, on the kinetics of the emulsifier-free emulsion polymerization of methyl methacrylate (MMA) and on the properties of the resulting poly(methy1 methacrylate) (PMMA) lattices were studied. The polymerizations were carried out using potassium persulfate (KPS) as the initiator. Monodisperse PMMA lattices with particle diameters varying between 0.14-0.37 pm and polymer molecular weights of the order 0.4 X lo6 to 1.2 X lo6 g/ mol were prepared. The initial rate of polymerization increases with increasing temperature, KPS-MMA mole ratio, EGDM content, or with decreasing ionic strength of the aqueous phase. It was shown that the bead size can be limited by reducing the monomer concentration or by using the cross-linking agent EGDM. The ionic strength of the aqueous phase has a dominant effect on final particle diameter and polymer molecular weight. The uniformity of the latex particles increases as the temperature increases or as the initiator concentration decreases. The experimental results can be reasonably interpreted by the homogeneous nucleation mechanism of the emulsifier-free emulsion polymerization of MMA. 0 1996 John Wiley & Sons, Inc.

Optical constants and fabrication parameters are investigated using surface plasmon resonance (SPR) studies on spun films of poly(methyl methacrylate) (PMMA) derivatives in contact with two different dielectric media. A value of 1.503 for the refractive index of PMMA films produced from a solution having concentration of 1 mg ml −1 at the speed of 3000 rpm is in close agreement with the data obtained from ellipsometric measurements. The film thickness shows a power-law dependence on the spin speed but the thickness increases almost linearly with the concentration of the spreading solution. These results are in good agreement with the hydrodynamic theory for a low-viscosity and highly volatile liquid. On the basis of SPR measurements under dynamic conditions, room temperature response of PMMA films to benzene vapours is found to be fast, highly sensitive and reversible. The sensitivity of detection of toluene, ethyl benzene and m-xylene is much smaller than that of benzene.

No abstract

No abstract

The aim of this study was to design polymeric nanospheres containing magnetic nanoparticle which could display superparamagnetic behavior and thus find application in allied fields. First magnetite nanoparticles were synthesized with coprecipitation method and then their stable acidic dispersion was prepared without surfactant and dropped into the polymerization system during a certain time interval after the polymerization started. The effects of time at which the magnetic sol was added into polymerization system on latex size and stability, average molecular weight of polymer were examined in the case of two different monomer concentrations. Extensive characterization by transmission electron microscopy, dynamic light scattering, thermal gravimetric analysis and magnetic measurements shows that when the magnetic sol was dropped during earlier time of polymerization at stage 1, the latex size, average molecular weight of polymer, thermal stability of polymeric composite, and saturation magnetization reduced, whereas polydispersity of size and molecular weight increased because of the reaction between persulfate and naked surface of magnetite at the aqueous phase.

The effects of the various salts onto the emulsifier‐free emulsion polymerization of methyl methacrylate (MMA) were investigated. It was found that the kind and amount of the salts were very effective on the polymerization even onto the polymeric products. It is known that the ionic strength of the electrolyte is effective for the polymerization. However, our investigation with the same ionic strength of different electrolyte produced the different effect on the polymerization. It was found that the Stokes radiuses of ions are very important for the reaction kinetics and type of the product. At the same electrolyte concentration, as increased Stokes radii of cation of salts that not react (the fragments of initiator, ions, etc.) in polymerization, polymerization rate and average molecular weight of polymer decreased, polymer particle diameter increased. In the case of Br− and SO4= the anions of the salt are also demonstrated some unexpected reactions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2494–2500, 2007