Suspension polymerization generalities

The curve obtained with PVC prepared by suspension polymerization generally indicated autocatalytic thermal dehydrochlorination, and the time required for 0.1 mole % decomposition was usually less than 35 minutes (Figure 1). When PVC was prepared by bulk polymerization, the dehydrochlorination plot was generally slightly more linear, showed little autocatalytic character, and the time for 0.1 mole % decomposition was approximately 40 minutes (Figure 2). 

Because the polymerization occurs totally within the monomer droplets without any substantial transfer of materials between individual droplets or between the droplets and the aqueous phase, the course of the polymerization is expected to be similar to bulk polymerization. Accounts of the quantitative aspects of the suspension polymerization of methyl methacrylate generally support this model (95,111,112). Developments in suspension polymerization, including acryUc suspension polymers, have been reviewed (113,114). 

Wheieas the BPO—DMA ledox system works well for curing of unsaturated polyester blends, it is not a very effective system for initiating vinyl monomer polymerizations, and therefore it generally is not used in such appHcations (34). However, combinations of amines (eg, DMA) and acyl sulfonyl peroxides (eg, ACSP) are very effective initiator systems at 0°C for high conversion suspension polymerizations of vinyl chloride (35). BPO has also been used in combination with ferrous ammonium sulfate to initiate emulsion polymerizations of vinyl monomers via a redox reaction (36). 

Styrene is a colorless Hquid with an aromatic odor. Important physical properties of styrene are shown in Table 1 (1). Styrene is infinitely soluble in acetone, carbon tetrachloride, benzene, ether, / -heptane, and ethanol. Nearly all of the commercial styrene is consumed in polymerization and copolymerization processes. Common methods in plastics technology such as mass, suspension, solution, and emulsion polymerization can be used to manufacture polystyrene and styrene copolymers with different physical characteristics, but processes relating to the first two methods account for most of the styrene polymers currendy (ca 1996) being manufactured (2—8). Polymerization generally takes place by free-radical reactions initiated thermally or catalyticaHy. Polymerization occurs slowly even at ambient temperatures. It can be retarded by inhibitors. 

Beaded acrylamide resins (28) are generally produced by w/o inverse-suspension polymerization. This involves the dispersion of an aqueous solution of the monomer and an initiator (e.g., ammonium peroxodisulfates) with a droplet stabilizer such as carboxymethylcellulose or cellulose acetate butyrate in an immiscible liquid (the oil phase), such as 1,2-dichloroethane, toluene, or a liquid paraffin. A polymerization catalyst, usually tetramethylethylenediamine, may also be added to the monomer mixture. The polymerization of beaded acrylamide resin is carried out at relatively low temperatures (20-50°C), and the polymerization is complete within a relatively short period (1-5 hr). The polymerization of most acrylamides proceeds at a substantially faster rate than that of styrene in o/w suspension polymerization. The problem with droplet coagulation during the synthesis of beaded polyacrylamide by w/o suspension polymerization is usually less critical than that with a styrene-based resin. 

Suspension polymerizations are often regarded as "mini-bulk" polymerizations since ideally all reaction occurs w ithin individual monomer droplets. Initiators with high monomer and low water solubility are generally used in this application. The general chemistry, initiator efficiencies, and importance of side reactions are similar to that seen in homogeneous media. 

The kinetics of termination in suspension polymerization is generally considered to be the same as for solution or bulk polymerization under similar conditions and will not be discussed further. A detailed discussion on the kinetics... 

Although solution polymerizations are typically employed, ROMP can also be carried out by bulk, emulsion, and suspension polymerization, and in a number of reaction media. Reaction efficiencies, molecular weights, and PDI values for ROMP of NBE and COE in supercritical CO2 using 10b, 22b, and 33a were generally similar to those... 

The section on suspension polymerization indicated the differentiation between suspension and emulsion (or latex) polymerizations. Emulsion polymers usually are formed with the initiator in the aqueous phase, in the presence of surfactants, and with polymer particles of colloidal dimensions, i.e., on the order of 0.1 gm in diameter [17]. Generally, the molecular weights of the polymers produced by an emulsion process are substantially greater than those produced by bulk or suspension polymerizations. The rate of polymer production is also higher. As a large quantity of water is usually present, temperature control is often simple. 

As manufactured, PTFE is of two principal types dispersion polymer, made by suspension polymerization followed by coagulation, and granular PTFE, polymerized and generally comminuted to a desirable particle size. Some details are given by Sperati. We have observed cast films of an aqueous colloidal dispersion and see that it consists of peanut-shaped particles, approximately 0.25 pm in size, which are composed of even finer particles. Electron micrographs of as-polymerized granular particles show three structures bands arranged in parallel, striated humps, and fibrils, some of which have the shish-kebab structure."... 

For the copolymerization of ethene and vinyl acetate, solution polymerization, suspension polymerization, emulsion polymerization and bulk polymerization may be used, but solution polymerization is preferred (1). A method of either continuous type or batch type may be employed. Methanol is generally used as the solvent. 

Materials. The polymer samples were prepared either by physical blending of PVC with an EVA copolymer or by suspension polymerization of vinyl chloride with the EVA copolymer dissolved in the monomer. The resulting dried polymer samples were blended with additives (organic Ba-Cd stabilizer and Pb-stearate) to the following general composition ... 

Even though monomers are generally quite reactive (polymerizable), they usually require the addition of catalysts, initiators, pH control, heat, and/or vacuum to speed and control the polymerization reaction that will result in optimizing the manufacturing process and final product.74 When pure monomers can be converted directly to pure polymers, it is called the process of bulk polymerization, but often it is more convenient to run the polymerization reaction in an organic solvent (solution polymerization), in a water emulsion (emulsion polymerization), or as organic droplets dispersed in water (suspension polymerization). Often choose of catalyst systems exert precise control over the structure of the polymers they form. They are referred to as stereospecific systems. 

Polymerizations of the monomer emulsions were carried out with oil-soluble initiators. Oil-soluble initiators have often been employed in emulsion polymerization recipes and are generally used in suspension polymerization. Whereas in the latter case the initiation naturally takes place in the monomer droplets, the locus of initiation and growth of particles in emulsion polymerization with oil-soluble initiators has been open to some doubt. However, the fact that the particle size and size distribution is not very different from the results with water-soluble initiators and that the particles are generally much smaller than the droplets in the monomer emulsions indicates that with... 

In general, the blowing agent can be added to the batch before or during the suspension polymerization [22]. It can also be incorporated into polystyrene that... 

These equations are perfectly general and therefore are applicable to solution, bulk, suspension, and emulsion polymerization systems. In the case of solution and bulk systems there is, in effect, only one particle with a volume of that of the whole reaction mixture. In emulsion and suspension polymerizations, the reaction mixture is subdivided into a large number of small particles and the influence of the state of subdivision is expressed by the factor z. 

The modeling of heterogeneous polymerization systems is generally more complicated than that of the homogenous systems because mass and heat transfer effects between two or more immiscible phases must be considered. Industrially important heterogeneous polymerization reactions include emulsion polymerization, suspension polymerization, precipitation polymerization, and solid-catalyzed olefin polymerization. The general polymerization rate equation is represented simply as... 

Dispersion in liquid/liquid L/L) systems is associated with the enlargement of the interface area between two immiscible liquids, so that e.g. an extraction process or a chemical reaction (saponification, nitration, etc.) can proceed rapidly or dispersions of particular droplet size are produced (bead and suspension polymerizations, etc.). In this chapter only dispersion by stirrers is considered. If this process is assisted by the addition of surface-active substances, it is termed emulsification, for which completely different laws generally apply, see e.g. [201]. 

The other major application of polymeric dispersants is in the preparation of solid/hquid dispersions (usually referred to as suspensions). In general, two methods are used for the preparation of suspensions condensation and dispersion methods ... 

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