Polymeric micelles particle size

By performing in situ the polymerization of acrylamide in water/AOT/toluene microemulsions, clear and stable inverse latexes of water-swollen polyacrylamide particles stabilized by AOT and dispersed in toluene have been found [192-194], It was shown that the final dispersions consist of two species of particles in equilibrium, surfactant-coated polymer particles (size about 400 A) with narrow size distribution and small AOT micelles (size about 30 A). 

Au NPs have been synthesized in polymeric micelles composed of amphiphilic block copolymers. Poly(styrene)-block-poly(2-vinylpyridine) in toluene has been used as nanocompartments loaded with a defined amount of HAuCl4 and reduced with anhydrous hydrazine. The metal ions can be reduced in such a way that exactly one Au NP is formed in each micelle, where each particle is of equal size between 1 and 15 nm [113]. In another example, the addition of HAuCfi to the triblock copolymer (PS-b-P2VP-b-PEO) (polystyrene-block-poly-2-vinyl pyridine-block-polyethylene oxide) permits the synthesis of Au N Ps using two different routes, such as the reduction of AuC14 by electron irradiation during observation or by addition of an excess of aqueous NaBH4 solution [114]. 

In many cases in drug development, the solubility of some leads is extremely low. Fast dissolution rate of many drug delivery systems, for example, particle size reduction, may not be translated into good Gl absorption. The oral absorption of these molecules is usually limited by solubility (VWIImann et al., 2004). In the case of solubility limited absorption, creating supersaturation in the Gl Luids for this type of insoluble drugs is very critical as supersaturation may provide great improvement of oral absorption (Tanno et al., 2004 Shanker, 2005). The techniques to create the so-called supersaturation in the Gl Luids may include microemulsions, emulsions, liposomes, complexations, polymeric micelles, and conventional micelles, which can be found in some chapters in the book. 

Yokoyama, M., Satoh, A., Sakurai, Y., et al. Incorporation of water-insoluble anticancer drug into polymeric micelles and control of their particle size. J. Contr. Rel. 55(2-3) 219-229. 1998. 

The description of phase 1 of the SE theory was refined by Gardon [133] and Harada et al. [134] the effect of particles in which polymerization has been terminated by radical entrance is included. Paris et al. [135] and Sautin et al. [136] calculate the balance of micelles and of the growing and dead particles. Pismen and Kuchanov [137] and Sundberg and Eliassen [138] included the effect of particle size distribution in their calculations. According to Fitch and Tsai [134] and Roe [140], the monomer swollen particles are produced by the polymerization of the monomer which is dissolved in water. 

Poehlein and Degraff [336] extended the derivation of Gershberg and Long-field [330] to the calculation of both molecular weight and particle size distribution in the continuous emulsion polymerization of St in a CSTR. On the other hand, Nomura et al. [163] carried out the continuous emulsion polymerization of St in a cascade of two CSTRs and developed a novel model for the system by incorporating their batch model [ 14], which introduced the concept that the radical capture efficiency of a micelle relative to a polymer particle was much lower than that predicted by the diffusion entry model (pocd -°). The assumptions employed were almost the same as those of Smith and Ewart (Sect. 3.3), except that the model did not assume a constant value of p. The elementary reactions and their rate expressions employed in the first stage are as follows ... 

We hav shown that with the use of a mixed surfactant system in styrene emulsion polymerization, the composition of the mixed surfactant has an effect on the rate of polymerization, the number of particles formed and the particle size distribution. We have also shown that a change in the ratio, r of the two surfactants in the mixture results in a considerable change in the micellar weight of the resultant mixed micelles. We have thus proposed and proven that the efficiency of nucleation of particles (even when the same number of micelles is used in the experiment) is dependent on the size of the mixed micelle, and that there is an optimum size at which the polymerization rate is the fastest and the particle size distribution is the narrowest. 

In this paper, a means is demonstrated for experimentally determining the percent of monomer conversion at which soap micelles disappear from the system during emulsion polymerization. By applying the mathematics and latex particle surface area which a soap molecule will occupy, developed for the soap titration particle size measurement procedure, the average particle size of the finished latex can be calculated. In fact, under some circumstances It might even be feasible to adjust monomer content. 

Materials and Polymerization. Styrene and methyl methacrylate were obtained from commercial sources and were distilled to remove inhibitor. After distillation, the monomers were stored, under nitrogen, in a refrigerator. For the mixed emulsifier system, Emulphogene BC840(GAF), tridecyloxy-polyethylene-oxyethanol, was used as the nonionic constituent, and sodium lauryl sulfate (K and K Labs) was used as the ionic constituent. The sodium lauryl sulfate was at a concentration below its cms whereas the BD-840 was at a concentration above its cmc. This emulsifier system has been shown to yield mixed micelles (2)/ having a low ionic change (2)/ which produce latlces with rather narrow particle size distributions (2 ) ... 

The surface activity of these compounds was not studied in detail. As mentioned in the Experimental Section, all were about equivalent in nucleating particles during emulsion polymerization. The resulting latexes when dialyzed to remove excess salt were stable against settling even at 10% solids over many months. Data on samples where both latex particle size and critical micelle concentration were measured is shown in Table II. 

Diffusion of the monomer from the micelles is prevented by the non-solvent properties of the outer phase. Therefore, the increase in particle size is negligible as the polymerization proceeds. 

---