Mini-emulsions

Mini-emulsion processes have been developed where the monomer is emulsified under high energy with either a long-chain alcohol or a polymer producing very small droplets. The long-chain alcohol retards the diffusion of the monomer out of the droplets (65). Polymerization takes place primarily... 

The red-luminescence (612 nm) europium complex is an excellent luminescer in commercial use however, the green-luminescence Tb +-cored dendrimer complex enables a simultaneous assay at another wavelength (545 nm). The latex formation was carried out by mini-emulsion radical polymerization of the monomers dissolving the Tb +-cored dendrimer complexes. The polymeriza-... 

Capek, I. and Chern, C.-S. Radical Polymerization in Direct Mini-Emulsion Systems. Vol. 155, pp. 101-166. 

Mini-emulsion poiymn. Micro-emulsion poiymn. 

Suspension polymerization may be the most important particle-forming polymerization from an industrial viewpoint. The system is very simple, composed of monomer, initiator, stabilizer, and medium (water in most cases). The monomer droplets with dissolving initiator are dispersed in water and the stabilizer exists at the interface. But suspension polymerization is regarded as a kind of homogeneous polymerization because the polymerization occurs only in monomer droplets and water does not affect the polymerization. Water contributes only to dividing the polymerization locus into small droplets and absorbing the heat evolved by polymerization. On the contrary, in emulsion polymerization, which is another type of polymerization performed in water and as practically important as suspension polymerization, water affects the polymerization significantly. In this section, emulsion polymerization is first discussed, and then some modified emulsion polymerizations such as soap-free emulsion polymerization and micro and mini emulsion polymerizations are described. 

McCaffery etal. discuss the use of a low-resolution Raman spectrometer to directly monitor a batch mini-emulsion polymerization.41 While this kind of equipment is unlikely to be installed in an industrial facility, the article raises several important points. In order to compensate for laser-power fluctuations, a functional group present in both the reactants and the product, the phenyl ring in styrene, was used as an internal standard. Since internal standards cannot be added to industrial reactions, this approach can be quite helpful. However, scientists must be certain that the internal standard will remain unchanged by the reaction and that changes in its signal only reflect laser-power fluctuations. 

A dispersion of droplets of one liquid in another, immiscible liquid, in which the droplets are of colloidal or near-colloidal sizes. The term can also refer to colloidal dispersions of liquid crystals in a liquid. Emulsions were previously referred to as emulsoids, meaning emulsion colloids. See also Macroemulsion, Mini-emulsion, Microemulsion. 

See Emulsion. The term is sometimes used to distinguish an emulsion from the microemulsion or micellar emulsion types. Thus a mini-emulsion would contain droplet sizes greater than 100 nm and less than 1000 nm, or some other specified upper-size limit. 

Aizpurua et al. [96] have studied the kinetics of vinyl acetate miniemulsions stabilized with PS or PVAc. Guyot and coworkers [97] used PS as the costabilizer for the mini emulsion encapsulation of pigment. Samer [67] has used PMMA to stabilize MMA miniemulsions for continuous polymerization in a CSTR. 

Various papers on hybrid mini emulsion polymerization have used alkyd [98, 99], polyester [100] or polyurethane [101] as both the costabihzer and a component of the hybrid particle. Since most of these materials were added far in excess of the levels normally used as costabihzers, it is not surprising that they are effective. 

However, this does not preclude mini emulsion copolymerization in a CSTR for extremely water-insoluble comonomers. In spite of the fact that the copolymer composition in the continuous miniemulsion is less than that predicted using the homogeneous copolymerization reactivity ratios, the miniemulsion copolymer might be more uniform than the macroemulsion copolymer, where the possibility of significant droplet nucleation could lead to two separate homopolymers or, at the very best, copolymers of various composition. Therefore, it is very important to use CSTR data to scale up a continuous miniemulsion copolymerization product to take into account the different particle growth kinetics for batch and continuous reactors. 

Wang et al. [98] carried out macroemulsion and mini emulsion polymerization of acrylic monomers in the presence of alkyd resins. Miniemulsion and macroemulsion polymers were produced using a commercial medium soya-linseed alkyd and a mix of acrylic monomers consisting of 50% BA, 49% MMA, and 1% acrylic acid (AA). PMMA polymer with a weight average molecular weight of 100,000 was used as the costabilizer. Alkyd levels were 5, 30, 60 or... 

Wang et al. [183] carried out hybrid mini emulsion polymerization of acrylates in the presence of polyurethane. The polyurethane was used as the costabilizer, and SLS as the surfactant. When MMA was used as the monomer, some homogenous nucleation was observed. This is in agreement with Tsavalas [179] who reported evidence of homogenous nucleation in the hybrid miniemulsion of MMA in the presence of alkyd. 

From the above summary of experimental investigations into Uving miniemulsion polymerization, we can see that controlled mini emulsion polymerization (SFRP, ATRP, and RAFT) is less colloidal-stable during polymerization than its non-living counterpart. Colloidal instability leads to phase separation in the worst cases. In improved cases, the latex that results from the controlled mini-... 

Barrere and Landfester [319] reported the synthesis of polyester in mini-emulsions. Hydrophobic polyesters were synthesized in miniemulsion. DBSA was used as a catsurf (catalyst and surfactant) and HD was used as the co-... 

The mechanism of this mini-emulsion emulsification process was investigated by the conductometric titration of aqueous hexadecyltrimethylammonium bromide-cetyl alcohol mixtures with benzene or styrene combined with transmission electron microscopic examination of the morphology of the mixed emulsifiers and the styrene droplets formed (2,8). Figure 1 shows that the titration curves with and without cetyl alcohol are quite different that for... 

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