Polymerizable cosurfactants

Two other investigations employed polymerizable cosurfactants. In one case [122], high-solid nanolatexes with size between 22 and 60 nm and solid... 

The products were polymers of methyl methacrylate, butyl acrylate, or their copolymer. The amount of surfactant was about 9% of the monomers and for the cosurfactant the feature was only 1 %. When the same surfactant was used with pentanol as cosurfactant or with no cosurfactant, the particle size distribution was much broader, even bimodal. The latexes were shown to be stable vs. electrolyte (aluminum sulfate), and also for several freeze-thaw cycles. These features were attributed more to the nature of the surfactant than to the use of polymerizable cosurfactant. 

While most vesicles are formed from double-tail amphiphiles such as lipids, they can also be made from some single chain fatty acids [73], surfactant-cosurfactant mixtures [71], and bola (two-headed) amphiphiles [74]. In addition to the more common spherical shells, tubular vesicles have been observed in DMPC-alcohol mixtures [70]. Polymerizable lipids allow photo- or chemical polymerization that can sometimes stabilize the vesicle [65] however, the structural change in the bilayer on polymerization can cause giant vesicles to bud into smaller shells [76]. Multivesicular liposomes are collections of hundreds of bilayer enclosed water-filled compartments that are suitable for localized drug delivery [77]. The structures of these water-in-water vesicles resemble those of foams (see Section XIV-7) with the polyhedral structure persisting down to molecular dimensions as shown in Fig. XV-11. 

Gan and Chew [37,38] extended their studies to microemulsions in which all the components except water were polymerizable. Polymerization in microemulsions containing a polymerizable surfactant (sodium acrylamidoundecanoate [37] or acrylamidostearate [38]), a cosurfactant (acrylic acid), and methyl methacrylate as the continuous phase led, under certain conditions, to transparent solid terpolymers with up to 10-20% water dispersed in the polymer matrices. As in the case of copolymers, no particular structure was shown by SEM for these terpolymers. 

The above example highlights the important role of a polymerizable surfactant or cosurfactant in microemulsion polymerization. Gan and Chew [38] were thus able to produce transparent solid polymers by fully polymerizing 54 % MMA, 34 % AA, 10 % H2O, and 2 % SDS or with other lower water concentrations. On further replacement of SDS by a polymerizable surfactant, sodium acrylamidoundecanoate [37], the resulting transparent solid polymers were still compatible with the similar amount of water. This prompted further studies on copolymerization in microemulsions of MMA, AA, and sodium acrylamidostearate (NaAAS), all the three components being readily polymerizable and amenable to terpolymerization in microemulsions. 

With regard to the behavior of polar polymers in microemulsions, it has been reported that polymerization in methyl methacrylate microemulsions with non-polymerizable surfactants and cosurfactants [28] leads to phase separation of the system in spite of the fact that the poly(methyl methacrylate) is soluble in its monomer. On the other hand, polar polymers such as amphiphilic block copolymers, e.g., poly(2-vinyl p5nidine-fc-ethylene oxide), have been used as cosurfactants to stabilize microemulsions [65, 66] and a specific mechanism has been proposed for polar polymers as stabilizers for emulsions and microemulsions [67]. 

Many kinds of polymerizable miniemulsion recipes have been described [9,85]. In the majority of the described systems, the emulsification is achieved by high-energy methods. The emulsifier in the earlier formulations [1] consisted of ionic surfactant/fatty alcohol (cosurfactant) mixtures. It was thought that the stabilizing mechanism was due to the presence of a protective interfacial complex. Later, it was shown that the replacement of the fatty alcohol by a highly hydrophobic compound (e.g., hexadecane) decreased more effectively the Ostwald ripening without the existence of any interfacial complex [9]. Different types of molecules such as reactive co-... 

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