| Porous polymer microspheres are widely researched and used as new active carrier systems in cosmetics or pharmaceuticals. Because of the large surface area and controllable porous structure, porous polymer microspheres have advantageous of sustained release of actives over prolong time to increase efficiency time, low toxicity to skin and favorable biocompatibility of the cosmetics systems. Poly (styrene-divinylbenzene) (PSt-DVB) microspheres are very efficient carrier materials because of their chemical stability in the entire pH range and stable porous structure. In this article, monodisperse PSt-DVB microspheres in the size range of 2~9μm are prepared by the modified two-step swelling and polymerization method. The produced porous microspheres are applied as a carrier to study the adsorption and release behaviors of cosmetic actives. The produced actives-carrying porous microspheres exhibit an effectively slow release behavior.The uniformity of PSt-DVB microspheres is one of the main factors to affect carrier efficiency. Such polymer microspheres are normally produced by suspension polymerization. However, the suspension process gives relatively large particles with a broad particle size distribution, even if the polymerization conditions are strictly controlled. The relatively uniform porous PSt-DVB microspheres in the size range of 10~50μm were prepared by modified suspension polymerization of styrene (St) with divinylbenzene (DVB) in the presence of toluene, cyclohexanol and heptane as porogenic diluents. In this paper, the use of ultrasonic dispersion decreased the beads'size and improved the uniformity. The effects of the porogen mixture, DVB content, the amount of dispersant and solvent extraction on the surface performance of the synthesized beads were studied. It was found that a great proportion of the non-solvating porogen increases the pore diameter and the specific surface area. High DVB concentration also results in the great specific surface area and porosity. The dispersant has advantageous to obtain uniform microspheres by increase the interface viscosity. In the experiment condition of this article, when the volume ratio of toluene/cyclohexanol is 1:2, DVB content is at the range of 40~60%, the amount of dispersant is 1.2% and methylene chloride was used as extractant, the beads with good spherical shape and pore size were obtained.Monodisperse PSt-DVB porous microspheres in the size range of 2~9μm were prepared by modified two-step swelling and polymerization method, the use of ultrasonic assistant dispersion reduced the swelling time from traditional 48h to 15～20h. The uniform polystyrene (PS) particles are synthesized by dispersion polymerization, the effects of the concentration of monomer, amount of initiator, amount of stabilizer, composition of medium and reaction temperature on particle distribution and diameter were systematically investigated. The optimized reaction conditions were obtained as following: the amount of initiator is 1.0% (wt), the amount of stabilizer is 6.0%(wt), the volume of St is 25ml (total reaction volume 125ml), reaction temperature is 70℃, the reaction medium is ethanol or ethanol/water (90/10). The monodisperse polystyrene particles in the range of 1.5~4μm were prepared under above condition. The obtained PS beads were used as the seed particles and swollen by the activated agent and monomers , then the monodisperse porous PSt-DVB microspheres in the size range of 2~9μm may be synthesized by the polymerization in 75℃for 24h. The effects of activated conditions, ultrasonic dispersion time, seed type, assistant porogen type, and DBP/Seed and DVB/Seed ratios on the performances of the produced porous microspheres were discussed. It was found that the DBP used as activated agent in 35℃swelling for 5~10h may achieve a good activated result. The PSt-DVB porous microspheres diameter and distribution were largely influenced by the PS characteristics. The surface area increased and the pore diameter decreased with the DBP/Seed and DVB/Seed ratios. When the ratios of DBP/Seed and DVB/Seed are 1.0ml/g and 8~10ml/g respectively, toluene or heptane as the assistant porogen, the aimed porous microspheres were obtained satisfactorily.By using hydroquinone, arbutin and avobenzone as model actives, the adsorption and release behaviors were discussed. It was found that the hydrophobic PSt-DVB porous microspheres had excellent adsorption ability to little nonpolar molecular hydroquinone. By introducing the MMA, the porous microspheres would become intermediate polar materials because of the occurrence of hydrophobic group and hydrophilic group, then the adsorption ability to polarity arbutin and avobenzone was increased. The produced actives-carrying microspheres exhibited a slow release behavior, the release of hydrophilic arbutin was much faster than parsol 1789 and hydroquinone with a burst effect.Several mathematical models of drug release were used to fit the release of cosmetic actives from porous microspheres. The first order model could fit all release profiles, and Higuchi model or zero order model may only fit the release profile for one of the mentioned actives. Parsol 1789 was studied as a model hydrophobic ingredient. By taking consideration of diffusion and dissolution effects, a new model was developed for description of the release behaviors. The model was used to fit the release profiles of the above three different actives, and the diffusion coefficient and dissolution rate constant were obtained. Based on the modeling study, the relationship of porous microspheres structure, actives performances and release behavior was found, hence a theoretical basis was provided to optimize the microsphere synthesis and desired actives release profile.
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