Miniemulsion polymerization kinetics

All the factors discussed here make miniemulsion polymerization kinetics very complicated, as shown by the rather scattered values of the kinetic parameters a, P, y and 8 obtained from the relationships Np [S] [I] and Rp [S] [I] (e.g., see Table 5.1 in this section and Table 1 in reference 11). The parameter Np is the number of latex particles per unit volume of water, Rp is the rate of polymerization, and [S] and [I] are the concentrations of surfactant and initiator in water, respectively. As expected, the rate of polymerization in common miniemulsion polymerization systems increases with increasing concentration of surfactant or initiator [11]. As to the influence of the concentration of costabilizer (hexadecane) on the miniemulsion polymerization kinetics, the experimental results reported in the literature are not conclusive [12]. The rate of polymerization may decrease with increasing concentration of hexadecane or this effect may be insignificant in nuniemul-sion polymerization. These conflicting observations can be attributed to the different concentrations of monomer in the monomer droplets and the varying droplet sizes (or droplet numbers) when the level of hexadecane used in stabilizing the miniemulsion is varied. 

The first interval is the interval of particle nucleation (interval I) and describes the process to reach an equilibrium radical concentration within every droplet formed during emulsification. The initiation process becomes more transparent when the rate of polymerization is transferred into the number of active radicals per particle n, which slowly increases to n 0.5. Therefore the start of the polymerization in each miniemulsion droplet is not simultaneous, so that the evolution of conversion in each droplet is different. Every miniemulsion droplet can be perceived as a separate nanoreactor, which does not interact with others. After having reached this averaged radical number, the polymerization kinetics is slowing down again and follows nicely an exponential kinetics as known for interval III in emulsion polymerization or for suspension polymer-... 

The polymerization kinetics is governed by the droplet size. Tang et al. found that the polymerization of styrene miniemulsions created by the microfluidizer was faster than that of miniemulsions created by the omnimixer [64]. This behavior can mainly be attributed to the different droplet size prior to polymerization. In the first case, the droplets are smaller than in the second case [65]. Fontenot and Schork observed similar behavior for MMA miniemulsions. With increasing shear and increasing concentration of surfactant, the polymerization rate increases [22]. This again can be explained by different sizes of the initial droplets. 

Wang and Schork [73] used PS, PMMA and PVAc as the costabilizers in miniemulsion polymerizations of VAc with PVOH as the surfactant. They found that, while PMMA and PS were effective kinetic costabihzers (at 2-4%wt on total monomer) for this system, PVAc was not. While the polymeric costabilizers did not give true miniemulsions, Ostwald ripening was retarded long enough for predominant droplet nucleation to take place. 

Both the mini- and macroemulsion copolymerizations of pMS/MMA tend to follow bulk polymerization kinetics, as described by the integrated copolymer equation. MMA is only slightly more soluble in the aqueous phase, and the reactivity ratios would tend to produce an alternating copolymer. The miniemulsion polymerization showed a slight tendency to form copolymer that is richer in the more water-insoluble monomer. The macroemulsion formed a copolymer that is slightly richer in the methyl methacrylate than the co-... 

The polymerization kinetics of BA/MAETAC macroemulsion and miniemulsion copolymerization was investigated with the interfacial redox initiator system. It was found that adding MAETAC had a complex effect on the polymerization kinetics of BA, as shown in Figs. 17 and 18 [170]. 

A polymerization kinetically resembles as an emulsion such that h is approximately one, with nucleation occurring in the small monomer droplets, a suspension like characteristic. An example of this phenomena is miniemulsion polymerization [31] which will be discussed in further detail in a later section of the paper. 

Dausend J, Musyanovych A, Dass M, et al. (2008) Uptake mechanism of oppositely charged fluorescent nanoparticles in HeLa cells. Macromol Biosci 8 1135-1143 Ziegler A, Landfester K, Musyanovych A (2009) Synthesis of phosphonate-functionalized polystyrene and poly(methyl methacrylate) particles and their kinetic behavior in miniemulsion polymerization. Colloid Polym Sci. http //dx.doi.Org/10.1007/s00396-009-2087-z Lorenz MR, Kohnle MV, Dass M, et al. (2008) Synthesis of fluorescent polyisoprene nanoparticles and their uptake into various cells. Macromol Biosci 8 711-727... 

Chem C-S, Liou Y-C (1999) Kinetics of styrene miniemulsion polymerization stabilized by nonionic surfactant/alkyl methacrylate. Polymer 40 3763-3772... 

Tong ZH, Deng YL (2008) Kinetics of miniemulsion polymerization of styrene in the presence of organoclays. Macromol Mater Eng 293 529-537... 

Choi et al. [S] used dilatometry to monitor the kinetics of styrene miniemulsion polymerizations employing not only varying KPS concentrations but, in addition, the oil-soluble initiator 2,2 -azobis(2-methyl butyronitrile) (AMBN). The latter was initially thou t to provide an increased probability of nucleating all monomer droplets considering that the main locus of initiator decomposition and subsequent ch growth would be in the monomer droplets. This, however, did not prove to be the case. 

In the case of vinyl chloride, the kinetics of miniemulsion polymerization is complicated by the fact that almost from the beginning of the reaction, two reaction zones inside the droplets need to be considered (1) a practically pure monomer phase of decreasing volume, and (2) a precipitated, monomer-swollen polymer phase which increases in volume with conversioa The general expression for the rate of polymerization (moles dm H2O) is... 

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