Vinyl alcohol polymerization

Alcohol production, 13 768, 798 Alcohol sulfates, 2 19, 20 rat oral LD50 values, 8 445 Alcohol sulfation, 23 536-537 Alcohol testing, 12 96 Alcoholysis, 10 490, 491, 499, 503 18 519 in silicone chemistry, 22 554 in vinyl alcohol polymerization, 25 608-609... 

Batch saponification, in vinyl alcohol polymerization, 25 610 Batch scale up, pilot plant, 79 460 Batch sequencing and logic control,... 

Belt-conveyor scales, 26 244—245 Belt filter press, 25 913 Belt saponification, in vinyl alcohol polymerization, 25 609-610 Benard instability, 11 764 Benazepril hydrochloride, molecular formula and structure, 5 149t Benchmark dose and margin-of-exposure method, 25 244... 

Commercial hybrid materials, silicon-based, 73 538—540 Commercial hydrazines, physical properties of, 73 565t Commercial hydrolysis, in vinyl alcohol polymerization, 25 609, 612t Commercial immunoassays, for clinical applications, 74 140 Commercial inks, 74 320 Commercial laundering, detersive systems for, 8 413t... 

Continuous reforming operations, 25 166 Continuous salt mining, 22 806 Continuous saponification, 22 737—738, 741 in vinyl alcohol polymerization, 25 609-610... 

Poly(vinyl alcohol) is a useful water soluble polymer It cannot be prepared directly from vinyl alcohol because of the rapidity with which vinyl alcohol (H2C=CHOH) isomenzes to acetaldehyde Vinyl acetate however does not rearrange and can be polymerized to poly(vinyl acetate) How could you make use of this fact to prepare poly(vinyl alcohol)" ... 

Other fairly recent commercial products, poly(vinyl amine) and poly(vinyl amine vinyl alcohol), have addressed the need for primary amines and their selective reactivity. Prior efforts to synthesize poly(vinyl amine) have been limited because of the difficulty hydrolyzing the intermediate polymers. The current product is prepared from /V-ethenylformamide (20) formed from the reaction of acetaldehyde and formamide. The vinyl amide is polymerized with a free-radical initiator, then hydrolyzed (eq. 7). 

Many of these reactions are reversible, and for the stronger nucleophiles they usually proceed the fastest. Typical examples are the addition of ammonia, amines, phosphines, and bisulfite. Alkaline conditions permit the addition of mercaptans, sulfides, ketones, nitroalkanes, and alcohols to acrylamide. Good examples of alcohol reactions are those involving polymeric alcohols such as poly(vinyl alcohol), cellulose, and starch. The alkaline conditions employed with these reactions result in partial hydrolysis of the amide, yielding mixed carbamojdethyl and carboxyethyl products. 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Vinyl alcohol does not exist as a monomer, but Herrmann and Haehnel (1) were able to obtain the desired product poly(vinyl alcohol) [9002-89-5] (PVA), by polymerizing vinyl acetate and then hydrolyzing the resultant poly(vinyl acetate). This process is employed for the commercial production of PVA even now. The principal concern of the discoverers was development of a suture for surgical operations the fiber then obtained was not suited for clothing use (2). 

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. 

Three generations of latices as characterized by the type of surfactant used in manufacture have been defined (53). The first generation includes latices made with conventional (/) anionic surfactants like fatty acid soaps, alkyl carboxylates, alkyl sulfates, and alkyl sulfonates (54) (2) nonionic surfactants like poly(ethylene oxide) or poly(vinyl alcohol) used to improve freeze—thaw and shear stabiUty and (J) cationic surfactants like amines, nitriles, and other nitrogen bases, rarely used because of incompatibiUty problems. Portiand cement latex modifiers are one example where cationic surfactants are used. Anionic surfactants yield smaller particles than nonionic surfactants (55). Often a combination of anionic surfactants or anionic and nonionic surfactants are used to provide improved stabiUty. The stabilizing abiUty of anionic fatty acid soaps diminishes at lower pH as the soaps revert to their acids. First-generation latices also suffer from the presence of soap on the polymer particles at the end of the polymerization. Steam and vacuum stripping methods are often used to remove the soap and unreacted monomer from the final product (56). 

Almost all synthetic binders are prepared by an emulsion polymerization process and are suppHed as latexes which consist of 48—52 wt % polymer dispersed in water (101). The largest-volume binder is styrene—butadiene copolymer [9003-55-8] (SBR) latex. Most SBRlatexes are carboxylated, ie, they contain copolymerized acidic monomers. Other latex binders are based on poly(vinyl acetate) [9003-20-7] and on polymers of acrylate esters. Poly(vinyl alcohol) is a water-soluble, synthetic biader which is prepared by the hydrolysis of poly(viayl acetate) (see Latex technology Vinyl polymers). 

Long-chain alcohols, such as are obtained by the hydrogenation of coconut oil, polymerization of ethylene, or the 0x0 process (qv), are sulfated on a large scale with sulfur thoxide or chlorosulfuhc acid to acid sulfates the alkaU salts are commercially important as surface-active agents (see Surfactants). Poly(vinyl alcohol) can be sulfated in pyhdine with chlorosulfuhc acid to the hydrogen sulfate (84). 

Issues to be considered in selecting the best stabilizing system are polymeric chain branching which increases with high temperature and the presence of some stabilizers, polydispersity of the particles produced, and grafting copolymerization, which may occur because of the reaction of vinyl acetate with emulsifiers such as poly(vinyl alcohol) (43,44). 

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. 

Solution Polymerization. Solution polymerization of vinyl acetate is carried out mainly as an intermediate step to the manufacture of poly(vinyl alcohol). A small amount of solution-polymerized vinyl acetate is prepared for the merchant market. When solution polymerization is carried out, the solvent acts as a chain-transfer agent, and depending on its transfer constant, has an effect on the molecular weight of the product. The rate of polymerization is also affected by the solvent but not in the same way as the degree of polymerization. The reactivity of the solvent-derived radical plays an important part. Chain-transfer constants for solvents in vinyl acetate polymerizations have been tabulated (13). Continuous solution polymers of poly(vinyl acetate) in tubular reactors have been prepared at high yield and throughput (73,74). 

The physical piopeities of poly(vinyl alcohol) aie highly coiielated with the method of piepaiation. The final piopeities are affected by the polymerization conditions of the parent poly(vinyl acetate), the hydrolysis conditions, drying, and grinding. Further, the term poly(vinyl alcohol) refers to an array of products that can be considered copolymers of vinyl acetate and vinyl alcohol. 

Solubility. Poly(vinyl alcohol) is only soluble in highly polar solvents, such as water, dimethyl sulfoxide, acetamide, glycols, and dimethylformamide. The solubiUty in water is a function of degree of polymerization (DP) and hydrolysis (Fig. 4). Fully hydrolyzed poly(vinyl alcohol) is only completely soluble in hot to boiling water. However, once in solution, it remains soluble even at room temperature. Partially hydrolyzed grades are soluble at room temperature, although grades with a hydrolysis of 70—80% are only soluble at water temperatures of 10—40°C. Above 40°C, the solution first becomes cloudy (cloud point), followed by precipitation of poly(vinyl alcohol). 

Urea and poly(vinyl alcohol) form a polymeric carbamate ester (123—126) ... 

Partially hydrolyzed poly(vinyl alcohol) grades are preferred because they have a hydrophobic /hydrophilic balance that make them uniquely suited for emulsion polymerization. The compatibUity of the residual acetate units with the poly(vinyl acetate) latex particles partly explains the observed stabilization effect. The amount of PVA employed is normally 4—10% on the weight of vinyl acetate monomer. The viscosity of the resulting latex increases with increasing molecular weight and decreasing hydrolysis of the PVA (318). 

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). 

Polymeric Calcium Phosphate Cements. Aqueous solutions of polymers such as poly(acryHc acid), poly(vinyl alcohol), gelatin, etc, and/or autopolymerizable monomer systems, eg, 2-hydroxyethyl methacrylate, glycerol dimethacrylate, calcium dimethacrylate, etc, have been used as Hquid vehicles (41,42,76) for the self-setting calcium phosphate cement derived from tetracalcium phosphate and dicalcium phosphate [7757-93-9J. 

Suspension Polymerization. This method (10) might be considered as a number of bulk polymerizations carried out simultaneously in the monomer droplets with water acting as a heat-transfer medium. A monomer-soluble initiator, eg, a peroxide or azo compound, and a protective coUoid like poly(vinyl alcohol) or bentonite, are requited. After completion of the polymerization, the excess of monomer(s) is steam stripped, and the beads of polymer are collected and washed on a centrifiige or filter and dried on a vibrating screen or by means of an expeUer—extmder. 

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