Polyvinyl suspension polymerization

In the suspension polymerization of PVC, droplets of monomer 30—150 p.m in diameter are dispersed in water by agitation. A thin membrane is formed at the water—monomer interface by dispersants such as poly(vinyl alcohol) or methyl cellulose. This membrane, isolated by dissolving the PVC in tetrahydrofuran and measured at 0.01—0.02-p.m thick, has been found to be a graft copolymer of polyvinyl chloride and poly(vinyl alcohol) (4,5). Early in the polymerization, particles of PVC deposit onto the membrane from both the monomer and the water sides, forming a skin 0.5—5-p.m thick that can be observed on grains sectioned after polymerization (4,6). Primary particles, 1 p.m in diameter, deposit onto the membrane from the monomer side (Pig. 1), whereas water-phase polymer, 0.1 p.m in diameter, deposits onto the skin from the water side of the membrane (Pig. 2) (4). These domain-sized water-phase particles may be one source of the observed domain stmcture (7). 

Beaded polymeric support, whether polystyrene-divinylbenzene, polymethacrylate, or polyvinyl alcohol, is conventionally produced by different variations of a two-phase suspension polymerization process, in which liquid microdroplets are converted to the corresponding solid microbeads (1). 

A process for the preparation of porous polyvinyl alcohol gels in three steps is (1) suspension polymerization of vinyl acetate with diethylene glycol dimethacrylate in the presence of a diluent as porogen, (2) saponifying of the resulting porous polyvinyl acetate gel with an alkali, and then (3) subjecting... 

A polyvinyl alcohol is obtained by suspension polymerization of vinyl acetate and the cross-linking agent, triallyl isocyanurate, with a triazine ring followed by alkali hydrolysis. The polyvinyl alcohol gel is used as packing for gel-... 

In suspension polymerization, the monomer gets dispersed in a liquid, such as water. Mechanical agitation keeps the monomer dispersed. Initiators should be soluble in the monomer. Stabilizers, such as talc or polyvinyl alcohol, prevent polymer chains from adhering to each other and keep the monomer dispersed in the liquid medium. The final polymer appears in a granular form. 

Figure 12-4. The European Vinyls Corp. process for producing polyvinyl chloride using suspension polymerization (1) reactor, (2) blow-down vessels (to separate unreacted monomer), (3) stripping column, (4) reacted monomer recovery, (5) slurry centrifuge, (6) slurry drier.

In suspension polymerization, the monomer is agitated in a solvent to form droplets, and then stabilized through the use of surfactants to form micelles. The added initiator is soluble in the solvent such that the reaction is initiated at the skin of the micelle. Polymerization starts at the interface and proceeds towards the center of the droplet. Polystyrene and polyvinyl chloride are often produced via suspension polymerization processes. 

Suspension polymerization. In this process, monomers and initiator are suspended as droplets in water or a similar medium. The droplets are maintained in suspension by agitation (active mixing). Sometimes a water-soluble polymer like methylcellulose or a finely divided clay is added to help stabilize or maintain the droplets. After formation, the polymer, is separated and dried. This route is used commercially for vinyl-type polymers such as polyvinyl chloride and polystyrene. 

In the suspension polymerization process, the autoclave reactor is filled with water. PVA, polyvinyl alcohol is the dispersing agent that helps stabilize the suspension. Lauroyl peroxide is the free radical catalyst that starts it all off. The reaction temperature is around 130°F, and the process takes 10—12 hours per batch, with 95% conversion. 

Monomer droplets are suspended in the water through the use of agitation and stabilizers, such as methyl cellulose, gelatin, polyvinyl alcohol, and sodium polyacrylate.32 Typical droplet sizes are 0.01-0.5 cm. A monomer soluble initiator is added to begin the polymerization. The kinetics of suspension polymerization are the same as for bulk polymerization, but suspension polymerization offers the advantage of good heat transfer. Polymers such as polystyrene, PVC, and polymethyl methacrylate are prepared by suspension polymerization. 

Polyvinyl chloride is produced by the free-radical polymerization of vinyl chloride. Bulk, emulsion, solution, and suspension polymerization processes have been used. 

Application A process to produce polyvinyl chloride (PVC) from vinyl chloride monomer (VCM) using suspension polymerization. Many types of PVC grades are produced including commodity, high K-value, low K-value, matted type and co-polymer PVC. The PVC possesses excellent product qualities such as easy processability and good heat stability. 

Vinnolit A process for making polyvinyl chloride by suspension polymerization. Developed by Vinnolit, Germany, and engineered by Uhde. Widely licensed worldwide. 

Application A process producing polyvinyl chloride (PVC) from vinyl chloride monomer (VCM) using suspension polymerization. 

There are four kinds of polymerization processes bulk, solution, emulsion, and suspension polymerization. As Table 4.7 shows [24], the heat of polymerization of vinyl acetate is high compared to other monomers hence, the control of temperature is difficult in bulk polymerization. In the case of emulsion and suspension polymerization, it is somewhat troublesome to separate dispersed polyvinyl acetate particles from the aqueous medium, and it is necessary to remove the emulsifier and stabilizer completely because these substances induce problems in the process of fiber-making. 

Hydrogenated cottonseed glyceride Hydrogenated palm glyceride dispersant, PVC suspension polymerization Polyvinyl alcohol dispersant, resins... 

Suspension polymerization occurs in water with the liquid monomer dispersed by agitaliorL The polymer is produced as a dispersed solid phase fiom polymerization of initiator-containing, 10 to 500 pm droplets under kinetics that match those of the bulk reaction of the monomer (7). The suspension is stabilized by insoluble organic or inorganic solids, electrolytes to increase monomer-water interfacial tension, and water soluble polymers that increase aqueous viscosity. Suspension polymerization is commonly used to synthesize two polymers covered in this book, polystyrene and polyvinyl chloride. 

Polyvinyl acetate (PVAc) is the largest volume polymer produced from a vinyl ester (1). In 1990, over 2.5 billion pounds of vinyl acetate monomer were produced in the United States alone (2). The bulk of this monomer was used for making PVAc and PVAc copolymers, which are widely used in water-based paints, adhesives, coatings, and binders for nonwoven paper products. PVAc is also the precursor to polyvinyl alcohol (PVA) and polyvinyl butyral, which cannot be made by direct polymerization. Methods of PVAc polymerization vary depending on the end use. Solution polymerizations of vinyl acetate in methanol are generally employed in processes in which PVAc is used as an intermediate in the production of PVA. PVAc latexes are generally made by emulsion polymerization, and PVAc in bead form is often synthesized by suspension polymerization (3,4). 

Water as diluent has obvious advantages and has been developed for many free-radical polymerizations. Thus suspension polymerization involves the dispersion of the non-miscible monomer in water as droplets (0.1-5 mm diameter) by means of agitation and protective colloids or dispersing agents (e.g. polyvinyl alcohol, PVAL), and adding a monomer-soluble initiator. The polymer ends up approximately the same size as the original droplets and the system can be viewed as many small bulk polymerizations. As water is the continuous phase the viscosity remains constant and good heat transfer occurs. This process is used for PVC. 

The term "suspension polymerization" is used traditionally for polymerization in a dispersed monomer phase. Occasionally the term is also u for the type of process described in the preceeding section, but for that the term "precipitation polymerization" is more appropiate. The polymerization in a dispersed monomer phase might also be called "dispersion polymerization", but this term is used for polymerizations where the monomer is originally dissolved, and the polymer is separated as a second liquid phase, usually absorbing some monomer. Suspension polymerization is used on a large scale for the manufacture of polyvinyl chloride (PVC), and for specific grades of polystyrene. 

Superabsorbent Polymers Superabsorbent polymers (SAP) are now commonly made from the polymerization of acrylic acid blended with sodium hydroxide in the presence of an initiator to form a poly-acrylic acid, sodium salt (sometimes referred to as cross-linked sodium polyacrylate). This polymer, such as polyacrylamide copolymer, ethylene maleic anhydride copolymer, cross-linked carboxy-methyl-cellulose, polyvinyl alcohol copolymers, cross-linked polyethylene oxide, and starch grafted copolymer of polyacrylonitrile to name a few. Superabsorbent polymers are made using one of two primary methods suspension polymerization or solution... 

Vinyl fluoride is an exception to almost all major fluorocarbon monomers in that there is only one commercial homopolymer and no copolymers. It is made by suspension polymerization. Polyvinyl fluoride (PVF) is fabricated into thin films by melt extrusion of its... 

Polyvinyl chloride resin is made from suspension polymerization of vinyl chloride monomer (Figure 4.21). 

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