Suspending agents poly

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

Common suspending agents are poly(vinyl alcohols) of various molecular weights and degrees of hydrolysis, starches, gelatin, calcium phosphate (especially freshly precipitated calcium phosphate dispersed in water to be used in the preparation), salts of poly(acrylic acid), gum arabic, gum tragacanth, etc. 

Procedure A. The autoclave was initially charged with about one-third of the total water used, which contained the entire amount of poly (vinyl alcohol) used as suspending agent and the crumbed copolymer after eliminating air by repeated washings with pure nitrogen, the monomer was introduced, and the mass was left to stand for 4 hours at room temperature. 

The styrene monomer first may be polymerized to about 65% conversion in the absence of water, and then the blowing agent (cyclopentane) may be added with additional peroxide. This solution is suspended in water in the presence of potato starch, and the polymerization is finished (74). By another modification a styrene solution of waste polystyrene and peroxide is suspended by poly (vinyl alcohol) in water, and pentane is added to the suspension after the solids content of the oil phase is greater than 70% (133). Polystyrene particles may also be suspended in water by a mixture of poly (vinyl alcohol) and a phenyl sulfonate and then a mixture of equal parts of pentane and catalyzed styrene (8% each on polymer) is diffused into the polymer. The temperature is elevated, and the polymerization is completed (23). 

A suspending agent unlikely to be modified by sulfur dioxide can be chosen among poly (vinyl alcohols) or cellulose derivatives. 

The suspension polymerization is conducted using monomer-soluble per-oxy initiators. Water-soluble polymers, such as poly(vinyl alcohol), are typically used as suspending agents to reduce the coalescence of the polymer particles [ 17]. A slurry of polymer particles 30-100 pm in diameter is formed during the polymerization. The particles are washed and dried before further processing. 

Porosity is a desirable characteristic of the particles in many applications of poly(vinyl chloride). If the product is to be used as a dry-blend resin, it is required to soak up substantial quantities of liquid plasticizers and still remain free-flowing. The structure and porosity of PVC granules is affected strongly by the choice of organic suspending agents, which are different types of partially hydrolyzed poly(vinyl alcohol). The required porosity is enhanced also by rapidly... 

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... 

While there have been many patents issued which deal with peripheral matters such as suspending agents and initiators, much of the published technology has advanced a little beyond that known by the end of World War II. As in the case of poly(vinyl chloride) technology, the chemistry of poly(vinyl... 

Typical suspending agents for the vinyl acetate polymerization are poly(vinyl alcohol) [particularly a grade represented as approximately 88% hydrolyzed poly(vinyl acetate)], gum arabic, hydroxyethyl cellulose, methyl cellulose, starches, sodium polyacrylate or sodium polymethacrylate, gelatin, and an equimolar copolymer of styrene and maleic anhydride neutralized with either sodium hydroxide or aqueous ammonia. Water-insoluble dispersing agents or... 

Sodium thiosulfate interfered with the polymerization in the aqueous phase. This manifested itself in a decrease in the overall rate of polymerization (cf. Table XVII). In this woric, substantial additions of sodiiun chloride were made to the aqueous phase to reduce further the unwanted emulsion polymerization. The suspending agent used in these experiments was a partially saponified poly(vinyl acetate) whose trade designation is Rhodoviol HS 100. This poly-(vinyl alcohol) was normally added to the reaction system as a 6% aqueous... 

One interesting aspect of this method of producing a suspension polymer is the fact that this method produces beads of poly(vinyl acetate) which may be loosely coated with poly(vinyl alcohol). This coating may be removed much more readily than the poly(vinyl alcohol) used in a conventional polymerization procedure. In the conventional process, a fair amoimt of the suspending agent probably forms a graft copolymer with vinyl acetate and is, therefore, permanently bound to the polymer bead. The properties of the two types of bead polymers are expected to be somewhat different since the graft copolymer with poly(vinyl alcohol) is present only in one and not the other polymer. 

The above condensation takes place in dichloroethane, with stannic chloride catalyst at 50 The maximum reaction rate varies with both the initial concentration of l,4-dimethyl-2,5-dichloro-methylbenzene, shown above, and the initial concentration of SnCU. Crosslinked polystyrene particles or beads also form by Friedel-Craft suspension crosslinking of polystyrene with l,4-dichloromethyl-2,5 dimethylbenzene The polymer is dissolved in nitrobenzene and a two-phase reaction occurs in 70% by weight of an aqueous suspension of ZnCh. Poly(vinyl alcohol) can be used as the suspending agent. 

Polyacrylamide ipa-le-o- kri-b- mld (1944) n. Poly(2-Propenamide) A non-ionic, water-soluble polymer prepared by the addition polymerization of acrylamide (CH2=CHC0NH2). The white polymer is readily soluble in cold water but insoluble in most organic solvents. It is used as a thickener, suspending agent, and as an ingredient in adhesives See image). 

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