Suspension polymerization, of vinyl acetate

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-... 

Suspension Polymerization of Vinyl Acetate (Control of Molecular Weight by... 

Suspension Polymerization of Vinyl Acetate in the Presence of Hydrogen... 

Probably most industrial homopolymerizations of vinyl acetate are carried out by suspension processes, since the resulting beads are readily converted to poly(vinyl alcohol). This is the major reason for producing the homopolymer. Surprisingly little has been published about the suspension polymerization of vinyl acetate, despite the fact that Lindemaim [1] cites nearly 1100 references on the subject of vinyl acetate and approximately 2(K) references on the higher vinyl esters. 

Suspension Polymerization of Vinyl Acetate (Control of Molecular Weight by Variation in Initiator Level) (Based on Bartl [4] and Bravar et al. [117])... 

A patented procedure for the suspension polymerization of vinyl acetate which is claimed to produce a nonsticky bead pol)mier [118] uses an aqueous phase consisting of 537 gm of distilled water, 0.25 gm gum tragacanth, and 0.10 gm sodium dioctylsulfosuccinate (Aerosol OT). The monomer charged consists of 690 gm of vinyl acetate and 0.69 gm of dibenzoyl peroxide. 

In a complex apparatus, Gimesch and Schneider [30, 119] studied the suspension polymerization of vinyl acetate. Their procedure involved equipment which automatically added tempered water to the reacting system as heat was evolved as a result of the polymerization process. Thus they maintained isothermal reaction conditions. The rate of reaction could be followed by recording the water uptake of the equipment with time. The heat of polymerization was also determined (found to be 23 kcal/mole which was considered a satisfactory check of the literature value which is scattered around 21.4 kcal/mole). From this work, a somewhat different mechanism of the suspension polymerization process emerges than the widely accepted concept of the water-cooled bulk polymerization of small particles. It was noted that with an increase in the initiator concentration, there was the expected increase in polymerization rate. With increasing stirring rate, the rate of polymerization decreased. Along with the suspension polymerization, there was always a certain amoimt of imdesirable emulsion polymerization. It was postulated that in the process, free radicals, formed in a monomer drop may be extracted into the aqueous phase where they may act on dissolved vinyl acetate by kinetic processes unique to this system and different from the conventional mechanism of suspension polymerization. 

TABLE XVII The Effect of the Agitation Rate on Yield and Bead Size in the Suspension Polymerization of Vinyl Acetate pOT... 

Uses Wetting agent, dispersant, emulsifier, penetrant, and solubilizer in emulsion and suspension polymerization of vinyl acetate for adhesives, paints, textile, fertilizer, mining, water treatment, fire fighting, cosmetic, food industries food pkg. adhesives, coatings, paper, cellophane, textiles emulsifier in mfg. of food-contact articles defoamer in food-contact paper/paperboard... 

Suspension Polymerization. At very low levels of stabilizer, eg, 0.1 wt %, the polymer does not form a creamy dispersion that stays indefinitely suspended in the aqueous phase but forms small beads that setde and may be easily separated by filtration (qv) (69). This suspension or pearl polymerization process has been used to prepare polymers for adhesive and coating appHcations and for conversion to poly(vinyl alcohol). Products in bead form are available from several commercial suppHers of PVAc resins. Suspension polymerizations are carried out with monomer-soluble initiators predominantly, with low levels of stabilizers. Suspension copolymerization processes for the production of vinyl acetate—ethylene bead products have been described and the properties of the copolymers determined (70). Continuous tubular polymerization of vinyl acetate in suspension (71,72) yields stable dispersions of beads with narrow particle size distributions at high yields. 

Polymerization of Vinyl Acetate in Suspension (Bead Polymerization)... 

Suspension Polymerization. The suspension or pearl polymerization process has been used to prepare polymers for adhesive and coaling applications and for conversion to poly(vinyl alcohol). Suspension polymerization are carried out with monomer-soiubie initiators predominantly, with low levels of stabilizers Continuous tubular polymerization of vinyl acetate in suspension yields stable dispersions of beads with narrow particle size distributions at high yields. 

Reichert, K. H. and Moritz, H. V., Continuous Polymerization of Vinyl Acetate in Suspension, J. Applied Polymer Science, Applied Polymer Symposium 36,151-164 (1981). 

Use Initiator for suspension polymerization of vinyl chloride solution polmyerization of various monomers such as acrylonitrile, MMA, vinyl acetate. 

Instead of low Mw surfactants or in combination with those natural or semisynthetic colloids are used in suspension polymerization of PVC and in emulsion polymerization of vinyl acetate homo- and co-polymers as protective colloids also called suspension stabilizers or suspending agents. 

A novel method of producing suspension polymers of poly(vinyl acetate) with a closely controlled molecular weight distribution involves the solution polymerization of vinyl acetate in methanol. By varying the ratio of monomer to methanol, a variety of molecular weight distributions may be prepared. The solution polymer is then added with agitation to an aqueous system containing poly(vinyl alcohol). The methanol is then distilled off to give a bead polymer [121]. 

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. 

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). 

Industrial suspension polymerizations of vinyl chloride are often carried out in large batch reactors or stirred jacketed autoclaves. Continuous reactors, however, have been introduced in several manufacturing facilities [315]. Typical recipes call for 100 parts of vinyl chloride for 180 parts of water, a suspending agent, like maleic acid-vinyl acetate copolymer, a chain transferring agent, and a monomer soluble initiator. The reaction may be carried out at 100 Ib/in. pressure and 50°C for approximately 15 h. As the monomer is consumed the pressure drops. The reaction is stopped at an... 

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