On the miniemulsion polymerization of very hydrophobic monomers initiated by a completely water‐insoluble initiator: thermodynamics, kinetics, and mechanism

Abstract

Successful miniemulsion polymerizations of very hydrophobic monomers, such as lauryl methacrylate and 4-tertbutyl styrene, initiated by very hydrophobic (i.e., completely water-insoluble) lauroyl peroxide, are reported. Conversion-time histories, as well as final latex properties, for example, the particle size distribution, are different from similar miniemulsion polymerizations in the presence of water-soluble initiators. The observed differences can be attributed to the average number of radicals inside a miniemulsion particle; the system obeys Smith-Ewart case I rather than Case II kinetics. Albeit the pairwise generation of radicals in the monomer droplets, substantial polymerization rates are observed. Water, present in the droplet interfacial layer, is supposed to act as chain transfer agent. The product of a chain transfer event is a hydroxyl radical, exit of this hydroxyl radical allows for the presence of single radicals in particles. The proposed mechanisms allow for agreement between initial droplet and final particle size distributions in miniemulsion polymerization initiated by lauroyl peroxide.

Incorporation of Very Insoluble Monomers in Waterborne Coatings

“…Amidst the properties of the binder, resistance to water is of particular relevance due to its pervasiveness in most applications, both in liquid and vapor form. Generally speaking, the water resistance of an emulsion polymer has been inversely related to the presence of hydrophilic components in the polymer matrix, and directly associated to the hydrophobic nature of the polymers produced . Among the hydrophilic species present in emulsion polymers, emulsifiers commonly make up the largest fraction.…”

“…Additional investigations involving the polymerization of very insoluble monomers, such as dodecafluoroheptyl methacrylate, 1H,1H,2H,2H‐perfluorodecyl acrylate, stearyl acrylate, and stearyl methacrylate have resulted in significant improvements in the water resistance of the polymers prepared. However, due to the extremely low water solubility of this kind of monomers (at least three orders of magnitude lower that styrene solubility in water), which has led to call them very insoluble monomers, these studies have been confined to high‐shear miniemulsion polymerization or working in high‐pressure systems . Other alternatives rely on using significant amounts of hydrophilic species to improve aqueous phase transport of the very insoluble monomers such as cyclodextrins, or using aqueous blends of organic solvents as the continuous phase .…”

“…However, due to the extremely low water solubility of this kind of monomers (at least three orders of magnitude lower that styrene solubility in water), which has led to call them very insoluble monomers, [10,11] these studies have been confined to high-shear miniemulsion polymerization or working in high-pressure systems. [12][13][14] Other alternatives rely on using significant amounts of hydrophilic species to improve aqueous phase transport of the very insoluble monomers such as cyclodextrins, [15,16] or using aqueous blends of organic solvents as the continuous phase. [17] However, these alternatives introduce their own sets of problems, such as the hydrophilic character of the cyclodextrins added that would remain on the final latex, or the additional separation stages necessary to eliminate the organic solvents used, that are considered volatile organic compounds (VOC) and should therefore be avoided.…”

“…Generally speaking, the water resistance of an emulsion polymer has been inversely related to the presence of hydrophilic components in the polymer matrix, and directly associated to the hydrophobic nature of the polymers produced. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Among the hydrophilic species present in emulsion polymers, emulsifiers commonly make up the largest fraction. Because of that, the use of polymerizable emulsifiers that would not be able to migrate through the polymer film has been regarded as an attractive alternative.…”

Synthesis of ethylene and butyl methacrylate‐based copolymer by emulsion polymerization

“…Consequently, due to the presence of a water soluble initiator and homogeneous heat transfer reaction, the polymer particles in emulsion polymerization can be stabilized by surfactants. This makes the emulsion polymerization an environment friendly process for the synthesis of high‐molecular‐weight polymers …”