Emulsion method

Vlayl fluoride undergoes free-radical polymerization. The first polymerization iavolved heating a saturated solutioa of VF ia tolueae at 67°C uader 600 MPa (87,000 psi) for 16 h (24). A wide variety of ioitiators and polymerization conditions have been explored (25—27). Examples of bulk (28,29) and solution (25,28,30,31) polymerizations exist however, aqueous suspension or emulsion methods are generally preferred (26,32—40). VF volatiflty dictates that moderately high pressures be used. Photopolymerizations, usually incorporating free-radical initiators, are also known (26,28,29,35). 

HomopolymeriZation. The free-radical polymeri2ation of VDC has been carried out by solution, slurry, suspension, and emulsion methods. 

The monomer, 2-chlorobuta-1,3-diene, better known as chloroprene, is polymerised by free-radical emulsion methods to give a polymer which is predominantly (-85%) fr<2 s-l, 4-polychloroprene but which also contains about 10% cii-1,4- 1.5%, 1,2- and 1% of 3,4-structures (Figure 11.17). The commercial polymers have a Tg of about -A3°C and a of about 45°C so that at usual ambient temperatures the rubber exhibits a measure of crystallinity. 

Recently, Mark and co-workers also reported on organophilic silica formed by the combination of the sol-gel procedure and water-in-oil micro-emulsion method, in which methacryloyloxypropyltrimethoxysilane was used as one component of silica matrix [8]. The size of the silica particle was controlled by the content of water and emulsifier used. The surface of the particles was effectively covered with methacryloyl. organic groups. This organophilic silica is expected to be used as a novel component of composite materials. 

Chain reactions are used to prepare a variety of high molar mass polymers of commericial importance and in practice may take one of four forms, namely bulk, solution, suspension, and emulsion methods. These four methods are described in the sections that follow, together with the loop modification which has become of commercial importance recently in producing latexes by emulsion polymerisation for the paint industry. 

Fig. 10 Preparation of antigen-encapsulating nanoparticles by w/o/w emulsion method...

Fig. 7 Preparation of water-soluble drug-loaded microspheres using w/o/w emulsion methods...

The addition of amphiphilic polymer in o/w or w/o/w emulsion systems is also useful to give surface functionality to MSs and NSs. Liang et al. reported preparation of NSs from poly(y-glutamic acid)-h-PLA, immobilizing galactose residues on the surface by an o/w emulsion method, and in vivo specific delivery of aniticancer... 

Micropsheres were successfully prepared using the PLGA-lysozyme conjugate by a single emulsion method. Encapsulation efficiency of lysozyme... 

Such an explanation cannot however account for the abnormally high values of the adsorption of simple salts at a water-oil interface, as found by Lewis. If we are to accept these results (though the emulsion method is certainly the least satisfactory of those used for the present purpose) some secondary effect must be looked for, such as the increased solubility of oil in water when emulsified and in the form of small particles. (The mean radius in one experiment was found to be about 4 x 10 cms., a size at which Hulett and Ostwald (see page 166) found a notable increase in the solubility of calcium and barium sulphates.) It is probable however that the chief error introduced was the disturbance brought about by the effect on the surface tension of the free charges of the salt ions (Lewis, Zeit. Physikal. Chem. Lxxiii. 129, 1910). (See Ch. VII.)... 

Moisture Content. 0.5% (max) when detd as specified in 4.3.1. When NG is used at the point of tnanuf in the production of propint by die water-slurry method or by the water emulsion method, the moisture requirement shall not apply... 

The water-in-oil-in-water (w/o/w) emulsion method (Figure 11.4) is the predominant method used for encapsulation of biomacromolecules in these microparticles. Protein solution forms the internal water phase of the w/o/w emulsion. Loading efficiency of the microparticles has not been optimal using water or buffer as an internal phase, so water is sometimes substituted with polymeric liquids, such as low molecular weight polyethylene glycol. The primary emulsion is then added to a secondary liquid phase, forming the secondary emulsion. The solvent for the... 

Vinyl acetate has been polymerized by bulk, suspension, solution, and emulsion methods. It copolymerizes readily with some monomers but not with others,... 

Homopolymerization. The free-radical polymerization of VDC has been carried out by solution, slurry, suspension, and emulsion methods. Slurry polymerizations are usually used only in the laboratory. The heterogeneity of the reaction makes stirring and heat transfer difficult consequently, these reactions cannot be easily controlled on a large scale. Aqueous emulsion or suspension reactions are preferred for large-scale operations. The spontaneous polymerization of VDC, so often observed when the monomer is stored at room temperature, is caused by peroxides formed from the reaction of VDC with oxygen, fery pure monomer does not polymerize under these conditions. Heterogeneous polymerization is characteristic of a number of monomers, including vinyl chloride and acrylonitrile. 

FIGURE 13.19 Drug loading of polymeric micelles by the dialysis (a) and the oil-in-water emulsion methods (b). (Reproduced from Jones, M. C. and J. C. Leroux. 1S90. J. Pharm. Biopharm48 101-111. With... 

The oil-in-water emulsion method consists Lrst of preparing an aqueous solution of the copolymer. To this a solution of the drug in a water-insoluble volatile solvent (e.g., chloroform is added to form an oil-in-water emulsion) (Jones and Leroux, 1999). The micelle-drug complex forms as the solvent evaporates. The main advantage of the dialysis procedure over this method is that potentially toxic solvents can be avoided. Both dialysis and oil-in-water emulsion methods were compared for the incorporation of DOX in PECb-PBLA micelles (Kwon et al., 1997). The emulsiLcation method was more efLcient with a DOX loading of 12% (w/w) (Kwon et al., 1997) compared with 8% (w/w) for the dialysis technique (Kwon etal., 1995). 

La et al. (1996) used the oil-in-water emulsion method to prepare IMC-incorporated micelles. Sixty mg of PEO-PBLA without drug was dissolved in 120 mL of distilled water and homogenized by sonication for 30 s. To the solution of PB PBLA micelle in distilled water, a chloroform solution of IMC (6 mg in 1.8 mL) was added drop wise under vigorous stirring at room temperature. The chloroform was removed by evaporation from the open system. The solution was then Lltered, using an Amicon YM-30 ultraLltration membrane (MWCO 50,000) to remove unbound IMC and low molecular weight contaminants, and lyophilized. 

If the syntheses are carried out in aqueous electrolytes containing sulfuric acid (emulsion method), product mixtures are generally obtained in poor yields 178). The electro-... 

Hydrolytic activities of free and immobilized lipase were assayed by the olive oil emulsion method according to the modification proposed by Soares et al. (11). One unit of enzyme activity was defined as the amount of enzyme that liberated 1 imol of free fatty acid/min under the assay conditions (37°C, pH 7.0,150 rpm). Analyses of hydrolytic activities carried out on the lipase loading solution and immobilized preparations were used to determine the activity-coupling yield (r %), which measures the recovered enzymatic activity according to Eq. 1 ... 

Li JK, Wang N, Wu XS (1998) Gelatin nanoencapsulation of protein/peptide drugs using an emulsifier-free emulsion method. J Microencapsul 15(2) 163-172... 

Yang, Y.-Y., Chung,T.-S., Bai, X.-L., and Chan, W.-K. (2000), Effect of preparation conditions on morphology and release profiles of biodegradable polymeric microspheres containing protein fabricated by double-emulsion method, Chem. Eng. Sci., 55, 2223-2236. 

Zambaux, M. F. (1998), Influence of experimental parameters on the characteristics of poly(lactic acid) nanoparticles prepared by a double emulsion method, J. Controlled Release, 50(1-3), 31-40. 

Two factors contribute to the stability of the gels prepared by the two-step concentrated emulsion. The repulsive forces between the charged surfactant molecules adsorbed on the surface of neighboring cells of the dispersed phase is one of them. The increased viscosity of the dispersed phase which contains the monomer constitutes the second factor, since the increased viscosity opposes the separation of the phases. The partial polymerization increases the viscosity of the dispersed phase, thus increasing the stability of the concentrated emulsion. Monomers that could not lead to gels in the one-step concentrated emulsion method were able to generate them when the two-step pathway was employed. Using this pathway, almost all monomers could be employed to prepare polymer materials. 

---