Type of Costabilizers in Miniemulsion Polymerization

Neglecting the effects of molar volume and interfacial tension, the following empirical equation can be used to reasonably predict the overall rate of Ostwald ripening for the monomer emulsion in the presence of costabiUzer [18]  

Alduncin et al. [28] studied the effect of a series of initiators with different water solubiUty (lauroyl peroxide, benzoyl peroxide, and 2,2 -azobisisobutyro-nitrile) on styrene emulsion polymerization. It was concluded that, among these oil-soluble initiators, only lauroyl peroxide with the lowest water solubility (2 X 10 g per 100 g water) is hydrophobic enough to stabilize the homogenized monomer emulsion against the degradation of monomer droplets by 

Chern et al. [33-39] used stearyl methacrylate or lauryl methacrylate as the reactive costabilizer to stabilize styrene miniemulsion polymerizations. Just like conventional costabilizers (e.g., hexadecane), long-chain alkyl methacrylates act as costabilizers in stabilizing the homogenized submicron monomer droplets. Furthermore, the methacrylate group (—C=C(CH3)COO—) of the polymerizable costabilizer can be chemically incorporated into latex particles in the subsequent free radical polymerization and thereby reduce the level of volatile organic compounds (VOC). As the polymerization proceeds, the reactive costabilizer concentration in the nucleated monomer droplets will decrease. The initial decrease of the costabilizer concentration should not cause any diffusional degradation because the hydrophobic polymer formed inside the nucleated monomer droplets can help stabilize the polymerizing miniemulsion. 

Those who are interested in the recipes (e.g., monomers, surfactants, costabilizers, and initiators), preparation (e.g., homogenization equipments and processes), and characterization (e.g., monomer droplet size and droplet size distribution and colloidal stability) of monomer miniemulsions are referred to references 12 and 13. 

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