Suspension polymerization, polymer manufacture

Compared with emulsion polymerization and suspension polymerization, the manufacturing process of suspension polymerization of inverse emulsion is more complicated. The advantage of using this technology is to make a capsular structure which has a polymer shell and liquid inner phase. The polymer shell can provide protection by preventing the inner phase from leaking out. When nanoparticles are added to the polymer shell, they can inhibit mass transfer and reinforce the polymer matrix to make the nanocomposites stronger or thermally stable. More importantly, the presence of nanoparticles can partially replace or completely eliminate the use of emulsifiers in the nanocomposite bead synthesis process. One application, as mentioned before, is to make PS nanocomposite... 

The discovery of PTFE (1) in 1938 opened the commercial field of perfluoropolymers. Initial production of PTFE was directed toward the World War II effort, and commercial production was delayed by Du Pont until 1947. Commercial PTFE is manufactured by two different polymerization techniques that result in two different types of chemically identical polymer. Suspension polymerization produces a granular resin, and emulsion polymerization produces the coagulated dispersion that is often referred to as a fine powder or PTFE dispersion. 

Processes that are essentially modifications of laboratory methods and that allow operation on a larger scale are used for commercial preparation of vinyhdene chloride polymers. The intended use dictates the polymer characteristics and, to some extent, the method of manufacture. Emulsion polymerization and suspension polymerization are the preferred industrial processes. Either process is carried out in a closed, stirred reactor, which should be glass-lined and jacketed for heating and cooling. The reactor must be purged of oxygen, and the water and monomer must be free of metallic impurities to prevent an adverse effect on the thermal stabiUty of the polymer. 

Manufacture of highly water-absorbent polymers with uniform particle size and good flowability can be carried out by reverse phase suspension polymerization of (meth)acrylic acid monomers in a hydrocarbon solvent containing crosslinker and radical initiator. Phosphoric acid monoester or diester of alka-nole or ethoxylated alkanole is used as surfactant. A polymer with water-absorbent capacity of 78 g/g polymer can be obtained [240]. 

Polystyrene is unusual among commodity polymers in that we can prepare it in a variety of forms by a diversity of polymerization methods in several types of reaction vessel. j Polystyrene may be atactic, isotactic, or syndiotactic. Polymerization methods include free radical, cationic, anionic, and coordination catalysis. Manufacturing processes include bulk, solution, suspension, and emulsion polymerization. We manufacture random copolymers ... 

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."... 

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. 

Two ASA polymers were studied Luran S 757R and Luran S 776S both were made by BASF. The polymers have similar SAN matrices but respectively contain ca. 30 and 40% of the acrylic rubber-toughening agent. The ABS polymer (ABS 500) was made by the Dow Chemical Co. It contained SAN-filled rubber particles ca. 1.0 /an in diameter, suggesting that it was manufactured by bulk or suspension polymerization. 

The commercial manufacture of polystyrene was batch mode through the 1930s and 1940s, with a gradual transition to continuous bulk polymerization beginning in the 1950s. Suspension polymerization was a common early polystyrene production process, where a single reactor produced a polymer slurry that had to be separated from the water and dried. This process was ideal for free radical... 

Suspension polymerization is frequently employed as the second stage following a preliminary bulk polymerization, such as in the manufacture of some HIPS and ABS polymers. Polybutadiene or another elastomer is dissolved in liquid styrene, and this monomer or a mixture of styrene and acrylonitrile is polymerized in a batch kettle. The syrup produeed at 30-35% conversion is too viscous for effective mixing and heat transfer. It is therefore dispersed in water, and the polymerization is finished as a suspension reaction. 

Aqueous dispersions of poly(vinyl acetate) and vinyl acetate-ethylene copolymers, homo- and copolymers of acrylic monomers, and styrene-butadiene copolymers are the most important types of polymer latexes today. Applications include paints, coatings, adhesives, paper manufacturing, leather manufacturing, textiles and other industries. In addition to emulsion polymerization, other aqueous free-radical polymerizations are applied on a large scale. In suspension polymerization a water-irnrniscible olefinic monomer is also polymerized. However, by contrast to emulsion polymerization a monomer-soluble initiator is employed, and usually no surfactant is added. Polymerization occurs in the monomer droplets, with kinetics similar to bulk polymerization. The particles obtained are much larger (>15 pm) than in emulsion polymerization, and they do not form stable latexes but precipitate during polymerization (Scheme 7.2). 

Cellulose ethers, more particularly methyl cellulose (MQ, methylhydroxypro-pyl cellulose (MHPC) and hydroxypropyl cellulose (HPC) are used as protective colloids also called primary suspending agents in suspension polymerization for the manufacturing of S-PVC. Their role is maintaining the particle size of the resin. Hydroxyethyl cellulose (HEC) is preferred for manufacturing of vinyl acetate emulsion polymers and as a thickening agent in dispersimi paints. 

Polymer processing can be of several types, including free radical, cationic, anionic, metal complex, or metal oxide catalyzed, as mentioned earlier [5], Polymers can be made by bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization techniques [5], The automotive chemist or design engineer working for an OEM should be aware of these various manufacturing processes, which polymers are made by which process, and what characteristics can be expected from the type of process. 

A number of important commercial resins are manufactured by suspension polymerization, including poly(vinyl chloride) and copolymers, styrene resins [general purpose polystyrene, EPS, high impact polystyrene (HIPS), poly(styrene-acrylonitrile) (SAN), poly(acrylonitrile-butadiene-styrene) (ABS), styrenic ion-exchange resins], poly(methyl methacrylate) and copolymers, and poly(vinyl acetate). However, some of these polymers rather use a mass-suspension process, in which the polymerization starts as a bulk one and, at certain conversion, water and suspending agents are added to the reactor to form a suspension and continue the polymerization in this way up to high conversions. No continuous suspension polymerization process is known to be employed on a... 

Polymers can be classified according to the techniques used during the polymerization of the monomer. In bulk polymerization, only the monomer (and possibly eatalyst and initiator, but no solvent) is fed into the reactor. The monomer undergoes polymerization, at the end of whieh a (nearly) solid mass is removed as the polymer product. As we shall see later, bulk polymerization is employed widely in the manufacture of condensation polymers, where reactions are only mildly exothermic and viscosity is mostly low thus enhancing ready mixing, heat transfer, and bubble elimination. Solution polymerization involves polymerization of a monomer in a solvent in which both the monomer (reactant) and polymer (product) are soluble. Suspension polymerization refers to polymerization in an aqueous medium with the monomer as the dispersed phase. Consequently, the polymer resulting from such a system forms a solid dispersed phase. Emulsion polymerization is similar to suspension polymerization but the initiator is located in... 

Different processes are nsed in industry for the manufacture of polymers by fi-ee-radical chain polymerization. Among them homogeneous bulk polymerization is economically the most attractive and yields products of higher purity and clarity. But it has problems associated with the heat of polymerization, increases in viscosity, and removal of unreacted monomer. This method is nevertheless used for the manufacture of PVC, polystyrene, and poly(methyl methacrylate). More common processes are homogeneous solution polymerization and heterogeneous suspension polymerization. 

Solution polymerization is used for the manufacture of polyethylene, polypropylene, and polystyrene, but by far the most widely used process for polystyrene and PVC is suspension polymerization. In the latter process (also known as bead, pearl, or granular polymerization because of the form in which the final products may be obtained), the monomer is dispersed as droplets (0.01-0.05 cm in diameter) in water by mechanical agitation. Various types of stabilizers, which include water-soluble organic polymers, electrolytes, and water-insoluble inorganic compounds, are added to prevent agglomeration of the monomer droplets. Each monomer droplet in the suspension constitutes a small bulk polymerization system and is transformed finally into a solid bead. Heat of polymerization is quickly dissipated by continuously stirring the suspension medium, which makes temperature control relatively easy. 

On the other hand, the emulsifier residues are difficult to remove from the polymer. They cause the product to become more hydrophilic, and the dielectric loss increases. Additionally, in emulsion polymerization of vinyl chloride, certain soaps can catalyze the subsequent elimination of HCl in the final product. If possible, therefore, the most readily saponifiable emulsifiers are used, polymerization is carried out with the minimum practical emulsifier concentration, or nonionogenic emulsifiers are used, or, in the manufacture of solid polymers, emulsion polymerization is replaced with bulk or suspension polymerization. 

In general, the suspension polymerization can be distinguished into two types, namely, the bead and powder suspension polymerization [4]. In the former process, the polymer is soluble in its monomer and smooth spherical particles are produced. In the later process, the polymer is insoluble in its monomer and, thus, precipitates out leading to the formation of irregular grains or particles. The most important thermoplastic produced by the bead suspension polymerization process is PS. In the presence ofvolatile hydrocarbons (C4—C6), foamable beads, the so-called EPS, are produced. On the other hand, PVC, which is the second largest thermoplastic manufactured in the world, is an example of the powder type suspension polymerization. 

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