Initial Conditions for Miniemulsion Polymerization Systems

The extremely hydrophobic costabilizer molecules are primarily present in the homogenized monomer droplets, and their concentration in the continuous aqueous phase is generally negligible. Initiators used in miniemulsion polymerization can be either water-soluble or oil-soluble. The loci in which 

The most important characteristic of miniemulsion polymerization is the transformation of the homogenized monomer droplets into latex particles via the capture of free radicals when a water-soluble initiator such as the persulfate initiator is used to initiate the free radical polymer reactions. However, this feature does not necessarily guarantee that the particle nucleation mechanisms other than monomer droplet nucleation can be ruled out. As will be shown later, previous studies dealing with nucleation of particle nuclei in miniemulsion polymerization often resulted in controversial conclusions. This subject is still open to discussion, and it represents a great challenge to polymer scientists. 

The following summarizes a general reaction scheme for the formation of particle nuclei in miniemulsion polymerization [13]  

Chem et al. [32, 37-39] used a water-insoluble dye as the molecular probe for the particle nucleation loci in styrene miniemulsion polymerizations stabilized by a surfactant concentration lower than its critical micelle concentration. 

Increasing the persulfate initiator concentration in miniemulsion polymerization promotes the formation of particle nuclei in the continuous aqueous phase (homogeneous nucleation) [36,43]. Both the number of latex particles originating from monomer droplet nucleation and the number of water-borne particles increase with increasing the surfactant concentration. It is noteworthy that particle nuclei formed via the micellar nucleation mechanism as expected may become important if the surfactant concentration is well above its critical micelle concentration [44,45]. 

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