Dispersion polymerization continuous phase

It could be shown that miniemulsion polymerization is a very suitable method for synthesis of amphiphilic copolymer of high homogeneity and for control of the primary sequence [117], Both direct and inverse miniemulsions can be formed by placing the same monomers in the dispersed or continuous phase, reciprocally. The high interfacial area of miniemulsions is expected to stimulate the change of the growing radical from one phase to the other and, therefore, the formation of copoly-... 

Emulsion polymerization is a heterogenous reaction process in which unsaturated monomers are dispersed in continuous phase with the aid of emulsifiers and polymerized by free-radical initiators. The resulting product is a dispersion of polymer particles, typically smaller than 1 pm in size, in water and is referred to as polymer latex. 

From the viewpoint of macrostructure, homo- and copolymers are generally defined as single-phase systems. Polyblends and composites are always classified as multiphase systems consisting of a polymeric continuous phase or matrix and of a dispersed phase. The latter can be either another polymer or any other foreign material such as glass fibers, fillers, or minerals. 

In a typical ASD, the drug (solute phase) is dispersed in an inert carrier (e.g., a polymeric continuous phase) with molecular level distribution being the most desirable. Depending on the interactions between drug and polymer and the method of preparation, the ASD may exist as a one-phase, two-phase, or mixed-phase system. In the one-phase system, the drug is immobilized within the polymer matrix at a molecular level such that it... 

When reaction takes place in both the dispersed and continuous phases, in spite of the low monomer solubility in water, the thermodynamic equilibrium between the continuous and dispersed phase is established before polymerization starts (Nzihou et al. 1997). A porogen can be used to increase the partition of a water soluble monomer in droplets when the continuous phase is water (Gokmen et al. 2012). 

Microemuisions containing ILs have drawn considerable interest in recent years [9-11] since the first report by Han et al. [12]. The use of IL as dispersed or continuous phase in microemuisions makes them attractive owing to their unusual solvent properties. Up till now, various kinds of IL-based microemuisions have been prepared, and their phase behaviors, microstructures, micropolarities, and thermodynamic and dynamic properties have been investigated. These microemuisions have shown promises in different fields, such as material synthesis, polymerization, biocatalysis, chemical reaction, drug release, protein extraction and capillary electrophoresis, etc. 

Monomer solubility in the continuous phase plays an important role in all of this. The rate at which oligomeric radicals grow depends on the concentration of monomer, while at the same time the solubility of the oligoradicals (which is a direct function of monomer solubility) affects how readily they self-nucleate or are captured. The partition of monomer between the disperse and continuous phases, either monomer-swollen micelles or particles, also depends on the solubility. A so-called "water-insoluble monomer will have a low concentration in the continuous phase and a high concentration in the micelles, with the result that pol3nnerlzation is slow in early stages unless micelles are present. For water-soluble monomers, micelles are unnecessary for rapid particle formation because polymerization can progress readily in the aqueous phase. 

A unique feature of in situ encapsulation technology is that polymerization occurs ia the aqueous phase thereby produciag a condensation product that deposits on the surface of the dispersed core material where polymerization continues. This ultimately produces a water-iasoluble, highly cross-linked polymer capsule shell. The polymerization chemistry occurs entirely on the aqueous phase side of the iaterface, so reactive agents do not have to be dissolved ia the core material. The process has been commercialized and produces a range of commercial capsules. 

Emulsion Polymerization. When the U.S. supply of natural mbber from the Far East was cut off in World War II, the emulsion polymerization process was developed to produce synthetic mbber. In this complex process, the organic monomer is emulsified with soap in an aqueous continuous phase. Because of the much smaller (<0.1 jira) dispersed particles than in suspension polymerization and the stabilizing action of the soap, a proper emulsion is stable, so agitation is not as critical. In classical emulsion polymerization, a water-soluble initiator is used. This, together with the small particle size, gives rise to very different kinetics (6,21—23). 

Because most widely used methods used to prepare classical styrene/divinylben-zene copolymers have always been based on suspension polymerization, it seemed logical that a series of porous PDVB gels using similar methodologies could be developed. In suspension polymerization, divinylbenzene is suspended as a dispersion of small droplets in a continuous phase of water and polymerized by classical free radical initiation. This process produces the spherical beads... 

Stable particles in sufficient number, all the oligo-radi-cals and nuclei generated in the continuous phase are captured by the mature particles, no more particles form, and the particle formation stage is completed. The primary particles formed by the nucleation process are swollen by the unconverted monomer and/or polymerization medium. The polymerization taking place within the individual particles leads to resultant uniform microspheres in the size range of 0.1-10 jjLvn. Various dispersion polymerization systems are summarized in Table 4. 

In interfacial polymerization, monomers react at the interface of two immiscible liquid phases to produce a film that encapsulates the dispersed phase. The process involves an initial emulsification step in which an aqueous phase, containing a reactive monomer and a core material, is dispersed in a nonaqueous continuous phase. This is then followed by the addition of a second monomer to the continuous phase. Monomers in the two phases then diffuse and polymerize at the interface to form a thin film. The degree of polymerization depends on the concentration of monomers, the temperature of the system, and the composition of the liquid phases. 

In 1994, we reported the dispersion polymerization of MM A in supercritical C02 [103]. This work represents the first successful dispersion polymerization of a lipophilic monomer in a supercritical fluid continuous phase. In these experiments, we took advantage of the amphiphilic nature of the homopolymer PFOA to effect the polymerization of MMA to high conversions (>90%) and high degrees of polymerization (> 3000) in supercritical C02. These polymerizations were conducted in C02 at 65 °C and 207 bar, and AIBN or a fluorinated derivative of AIBN were employed as the initiators. The results from the AIBN initiated polymerizations are shown in Table 3. The spherical polymer particles which resulted from these dispersion polymerizations were isolated by simply venting the C02 from the reaction mixture. Scanning electron microscopy showed that the product consisted of spheres in the pm size range with a narrow particle size distribution (see Fig. 7). In contrast, reactions which were performed in the absence of PFOA resulted in relatively low conversion and molar masses. Moreover, the polymer which resulted from these precipitation... 

As another case study a process synthesis of an emulsion polymerization process is given (Hurme and Heikkila, 1998). In emulsion polymerization unsaturated monomers or their solutions are dispersed in a continuous phase with the aid of an emulsifier and polymerized. The product is a dispersion of polymers and called a latex. The raw materials are highly flammable unsaturated hydrocarbons and the reaction is exothermic which both cause a risk. The main phases and systems in an emulsion polymerization plant are listed in Table 31. 

In dispersion polymerization, the monomer and initiator are dissolved in the continuous phase, which acts as a nonsolvent for the developing polymer. The continuous phase can be organic, aqueous, or a mixture of miscible phases. Two methods of initiation have been employed, including gamma radiation [75] and chemical initiation by potassium perox-odisulphate [76]. As the polymer is formed, it precipitates as nanoparticles. These particles are not polymeric precipitates as in precipitation polymerization. Rather, they are swollen by a mixture of the monomer and the continuous phase [39],... 

A high internal phase liquid-liquid emulsion (HIPE) is one where the internal or dispersed phase droplets occupy >74% of the total volume of the emulsion. At this point the droplets contact each other and beyond this volume % the droplets are forced into distorted polyhedra. If for example styrene and divinylbenzene are employed as the continuous phase and water droplets dispersed in this oil phase using a suitable surfactant to form a HIPE, the comonomers can be polymerized to form a poly(styrene-divinylbenzene) polyHIPE. Typically the water droplets are... 

In contrast to the highly interconnected pores mentioned previously, closed pores can also be obtained by microemulsion polymerization if the initial volume fraction of the dispersed phase is kept lower than 30%. Recently two systems have been reported where the polymerization of the continuous phase and the subsequent removal of the Hquid dispersed phase resulted in the formation... 

Relationship Between Nodular and Rejecting Layers. Nodular formation was conceived by Maler and Scheuerman (14) and was shown to exist in the skin structure of anisotropic cellulose acetate membranes by Schultz and Asunmaa ( ), who ion etched the skin to discover an assembly of close-packed, 188 A in diameter spheres. Resting (15) has identified this kind of micellar structure in dry cellulose ester reverse osmosis membranes, and Panar, et al. (16) has identified their existence in the polyamide derivatives. Our work has shown that nodules exist in most polymeric membranes cast into a nonsolvent bath, where gelation at the interface is caused by initial depletion of solvent, as shown in Case B, which follows restricted Inward contraction of the interfacial zone. This leads to a dispersed phase of micelles within a continuous phase (designated as "polymer-poor phase") composed of a mixture of solvents, coagulant, and a dissolved fraction of the polymer. The formation of such a skin is delineated in the scheme shown in Figure 11. 

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