Polymerization aqueous suspension

Fluoropolymers are typically synthesized in aqueous polymerization systems (both emulsion and suspension), non-aqueous systems (Freon-113), or Freon-113/aqueous hybrid systems [8]. Such processes require the use of large quantities of water and CFCs (for non-aqueous polymerizations) or fluorinated surfactants (for emulsion polymerization). Aqueous suspension and dispersion poly-... 

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). 

A polymeric composition for reducing fluid loss in drilling muds and well cement compositions is obtained by the free radical-initiated polymerization of a water-soluble vinyl monomer in an aqueous suspension of lignin, modified lignins, lignite, brown coal, and modified brown coal [705,1847]. The vinyl monomers can be methacrylic acid, methacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, vinylacetate, methyl vinyl ether, ethyl vinyl ether, N-methylmethacrylamide, N,N-dimethylmethacrylamide, vinyl sulfonate, and additional AMPS. In this process a grafting process to the coals by chain transfer may occur. 

In the discussion above it has been shown that the lipid can been polymerized through UV irradiation of its aqueous suspension. The polymerization of the system improves the stability of the synthetic liposomes. Since there is an acetal linkage introduced between the polymer chain and the amphiphilic structure, this linkage can be slowly hydrolyzed in aqueous systems to separate the polymer chain from the lipid. 

Teflon is made by polymerizing tetrafluoroethylene in aqueous suspension. 

The results of polymerizations using these various initiators are shown in Table 6.4. The best results were obtained with FC-8 thus a number of aqueous suspension polymerizations were run under a variety of conditions using FC-8 dissolved and fed to the reaction in several different solvents. The results are shown in Table 6.5. The low yields are probably due to precipitation, premature decomposition in the feed line, or hydrolysis of the FC-8 peroxide prior to... 

The procedure chosen for the preparation of lipid complexes of AmB was nanoprecipitation. This procedure has been developed in our laboratory for a number of years and can be applied to the formulation of a number of different colloidal systems liposomes, microemulsions, polymeric nanoparticles (nanospheres and nanocapsules), complexes, and pure drug particles (14-16). Briefly, the substances of interest are dissolved in a solvent A and this solution is poured into a nonsolvent B of the substance that is miscible with the solvent A. As the solvent diffuses, the dissolved material is stranded as small particles, typically 100 to 400 nm in diameter. The solvent is usually an alcohol, acetone, or tetrahydrofuran and the nonsolvent A is usually water or aqueous buffer, with or without a hydrophilic surfactant to improve colloid stability after formation. Solvent A can be removed by evaporation under vacuum, which can also be used to concentrate the suspension. The concentration of the substance of interest in the organic solvent and the proportions of the two solvents are the main parameters influencing the final size of the particles. For liposomes, this method is similar to the ethanol injection technique proposed by Batzii and Korn in 1973 (17), which is however limited to 40 mM of lipids in ethanol and 10% of ethanol in final aqueous suspension. 

Crawford and co-workers were the first to study in detail the action of two streptomyces, S. badius 252 and S. viridosporus T7A, on lignocellulose from different sources. Their work led to the conclusion that the bacterial action on aqueous suspensions of these lignocellulosics resulted in the solubilization of lignin fragments which precipitate upon acidification Acid Precipitable Polymeric Lignin (APPL) (1-10). 

Viscosity of Polymer Solutions. Polymer solutions are very common. Glues, pastes, and paints are just a few examples of commercially available aqueous suspensions of organic macromolecules. Also, recall from Chapter 3 that certain types of polymerization reactions are carried out in solution to assist in heat removal. The resulting polymers are also in solution, and their behavior must be fully understand in order to properly transport them and effect solvent removal, if necessary. 

For example, an aqueous suspension homopolymerization would normally not be appropriate for water-soluble monomers such as acrylamide or acrylic acid. For such cases, it may be possible that with high levels of neutral salts, the water solubility of such monomers may be reduced to permit the use of suspension polymerization techniques. Other monomers may have other unique properties that require some modifications of the basic procedures. 

PAA can be prepared using bulk polymerization, aqueous polymerization, nonaqueous polymerization, inverse phase emulsion and suspension polymerization. The precise structure of the resulting PAA chain is dependent upon many factors including the polymerization process and conditions. The tacticity of... 

This interpretation poses an interesting question if vitreous silica behaves like polymeric silicic acid or silica gel in aqueous suspension, how do the crystalline modifications of silica interact with aqueous solutions ... 

Among the various techniques of grafting vinyl chloride described in the literature (1), we chose the one based on the polymerization, in aqueous suspension, of vinyl chloride in the presence of the backbone polymer with an organic peroxide. Some important improvements in this technique are the main subject of this paper. 

Today, a large part of the more than one billion lbs/year of impact polystyrene and 500 million lbs/year of ABS produced domestically is made by graft copolymerization. Impact polystyrene may be synthesized by dissolving a diene rubber in styrene monomer, in the presence or absence of another solvent, prepolymerizing the solution, and completing the polymerization in bulk, solution, or suspension. R. B. dejong describes a process wherein he prepolymerizes in emulsion with styrene as the continuous phase and the water as the dispersed phase and completes polymerization in aqueous suspension. 

Figure 2. EPR grafted vs. reaction time for polymerization in aqueous suspension. Procedure A T = 70°C BztOt = 0.38% ...

The polymerization reaction in aqueous suspension of vinyl chloride in the presence of an ethylene-propylene saturated elastomer occurs with the formation of poly (vinyl chloride) homopolymer and rubber-poly (vinyl chloride) grafted copolymers. The first grafting reaction proceeds as far as diffusion of the monomer inside the particles in suspension is possible afterwards, some chain branching of grafted PVC is possible. Under our experimental conditions the amount of grafted rubber does not exceed 60% of the initial rubber and is little influenced by the type of initiator used. 

However, polyphosphazene micelles are known. These are formed by sonication of aqueous suspensions of amphiphilic diblock copolymers—macromolecules in which one block is hydrophilic and the other is hydrophobic. Both blocks may be phosphazene-based, or one block can be a phosphazene and the other an organic polymer. Polymers of this type are assembled via the living cationic polymerization discussed earlier. The polymers shown as 3.95-3.99 illustrate the range of structures that have been studied and the size of the micelles formed.237-240... 

Aqueous suspension polymerization requires the usual additives, such as free radical initiators, colloidal dispersants (not always), and chain transfer agents to control molecular weight. After the process is completed, the suspension contains spherical particles approximately 100 pm in diameter. Suspension polymers are available as free-flowing powder or in pellet form for extrusion or injection molding.58... 

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