Competitive seed polymerization

A theoretical treatmerrt of competitive seed polymerization initiated by oil-soluble initiators has recently been given by M0rk [74]. The third-order... 

One of the problems with macroemulsion polymerization is the variability of the particle number with initiation rate, monomer quality, inhibition levels, and so on. This is a serious industrial problem, as shown by the fact that a great many industrial macroemulsion polymerizations are carried out as seeded polymerizations in which a known concentration of seed particles are added to the emulsion, and the polymerization is rim under conditions that suppress nucleation of additional particles. The variance in particle number comes about because there is a competition for surfactant between the growth of existing particles (that need additional surfactant to stabihze their growing surface area), and the nucleation of new particles. 

Seeded polymerization using a monodisperse seed latex allows the preparation of larger monodisperse latexes of different size (31). Indeed, such polymerizations can give sharpening of the particle size distribution (32,33). This self-sharpening tendency can be seen in competitive growth experiments (33,34) in which a mixture of two monodisperse latexes is used as the seed latex, so that the different-size particles compete for the available monomer and free radicals. Assuming that the rate of increase of the particle volume V with time is proportional to some power of the particle diameter... 

The desire to minimize this competitive oligomerization has motivated research into alternative means to decrease the polydispersity and simultaneously increase the molecular weight of the seed-oil derived polyols. Recent patents [128, 129] investigate an approach previously demonstrated for the hydroformylated polyols [130-132], i.e., hydroxylation of the fatty acid alkyl ester followed by polymerization from a petrochemically derived initiator molecule. Inventors state that this approach provides an improvement over previous epoxidized/hydroxylated polyols by allowing better control of the molecular weight and the functionality of the polyol products. 

Emulsion polymerization is the polymerization technique that starts with emulsified monomer in the continuous aqueous phase. Polymer formation takes place in the micelles and is initiated by water-soluble initiators. The monomers are insoluble or sparingly soluble in water. Emulsion polymerization is used very frequently in order to perform encapsulation of inorganic particles with polymers where water-based coatings are required. For the encapsulation of inorganic particles, seeded emulsion polymerization is performed hydrophobic inorganic particles are dispersed with normal surfactants or protective colloids in the aqueous phase. As polymerization on the surface of inorganic particles is always in competition with secondary particle formation, the concentration of the surfactants should be lower than their critical micelle concentration. However, homogeneous nucleation can also occur, which... 

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