Poly limitations

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). 

Historically, the development of the acrylates proceeded slowly they first received serious attention from Otto Rohm. AcryUc acid (propenoic acid) was first prepared by the air oxidation of acrolein in 1843 (1,2). Methyl and ethyl acrylate were prepared in 1873, but were not observed to polymerize at that time (3). In 1880 poly(methyl acrylate) was reported by G. W. A. Kahlbaum, who noted that on dry distillation up to 320°C the polymer did not depolymerize (4). Rohm observed the remarkable properties of acryUc polymers while preparing for his doctoral dissertation in 1901 however, a quarter of a century elapsed before he was able to translate his observations into commercial reaUty. He obtained a U.S. patent on the sulfur vulcanization of acrylates in 1912 (5). Based on the continuing work in Rohm s laboratory, the first limited production of acrylates began in 1927 by the Rohm and Haas Company in Darmstadt, Germany (6). Use of this class of compounds has grown from that time to a total U.S. consumption in 1989 of approximately 400,000 metric tons. Total worldwide consumption is probably twice that. 

Chlorine cannot be stored economically or moved long distances. International movements of bulk chlorine are more or less limited to movements between Canada and the United States. In 1987, chlorine moved in the form of derivatives was 3.3 million metric tons or approximately 10% of total consumption (3). Exports of ethylene dichloride, vinyl chloride monomer, poly(vinyl chloride), propylene oxide, and chlorinated solvents comprise the majority of world chlorine movement. Countries or areas with a chlorine surplus exported in the form of derivatives include Western Europe, Bra2il, USA, Saudi Arabia, and Canada. Countries with a chlorine deficit are Taiwan, Korea, Indonesia, Vene2uela, South Africa, Thailand and Japan (3). 

The limiting oxygen index of Tefzel as measured by the candle test (ASTM D2863) is 30%. Tefzel is rated 94 V-0 by Underwriters Laboratories, Inc., in their burning test classification for polymeric materials. As a fuel, it has a comparatively low rating. Its heat of combustion is 13.7 MJ/kg (32,500 kcal/kg) compared to 14.9 MJ /kg (35,000 kcal/kg) for poly(vinyHdene fluoride) and 46.5 MJ /kg (110,000 kcal/kg) for polyethylene. 

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. 

Bulk Polymerization. This is the method of choice for the manufacture of poly(methyl methacrylate) sheets, rods, and tubes, and molding and extmsion compounds. In methyl methacrylate bulk polymerization, an auto acceleration is observed beginning at 20—50% conversion. At this point, there is also a corresponding increase in the molecular weight of the polymer formed. This acceleration, which continues up to high conversion, is known as the Trommsdorff effect, and is attributed to the increase in viscosity of the mixture to such an extent that the diffusion rate, and therefore the termination reaction of the growing radicals, is reduced. This reduced termination rate ultimately results in a polymerization rate that is limited only by the diffusion rate of the monomer. Detailed kinetic data on the bulk polymerization of methyl methacrylate can be found in Reference 42. 

Attempts have been made to use cold-set adhesives in the cormgating operation, such as poly(vinyl acetate) and modified, precooked starch formulations, but these have not achieved any appreciable degree of commercial acceptance (20). The use of a polyethylene film appHed to the inside surface of the linerboard facing, which serves as a hot-melt cormgator adhesive, has achieved some commercial usage. However, its use is limited to the small, specialty product niche of fast-food hamburger cartons (see Olefin polymers, polyethylene). 

Tempera.ture Effect. Near the boiling point of water, the solubiUty—temperature relationship undergoes an abmpt inversion. Over a narrow temperature range, solutions become cloudy and the polymer precipitates the polymer caimot dissolve in water above this precipitation temperature. In Figure 4, this limit or cloud point is shown as a function of polymer concentration for poly(ethylene oxide) of 2 x 10 molecular weight. 

Fig. 4. Upper temperature limit for solubiUty of poly(ethylene oxide) in water. Molecular weight is 2 x 10 (3).

When equal amounts of solutions of poly(ethylene oxide) and poly(acryhc acid) ate mixed, a precipitate, which appears to be an association product of the two polymers, forms immediately. This association reaction is influenced by hydrogen-ion concentration. Below ca pH 4, the complex precipitates from solution. Above ca pH 12, precipitation also occurs, but probably only poly(ethylene oxide) precipitates. If solution viscosity is used as an indication of the degree of association, it appears that association becomes mote pronounced as the pH is reduced toward a lower limit of about four. The highest yield of insoluble complex usually occurs at an equimolar ratio of ether and carboxyl groups. Studies of the poly(ethylene oxide)—poly(methacryhc acid) complexes indicate a stoichiometric ratio of three monomeric units of ethylene oxide for each methacrylic acid unit. 

Other blends such as polyhydroxyalkanoates (PHA) with cellulose acetate (208), PHA with polycaprolactone (209), poly(lactic acid) with poly(ethylene glycol) (210), chitosan and cellulose (211), poly(lactic acid) with inorganic fillers (212), and PHA and aUphatic polyesters with inorganics (213) are receiving attention. The different blending compositions seem to be limited only by the number of polymers available and the compatibiUty of the components. The latter blends, with all natural or biodegradable components, appear to afford the best approach for future research as property balance and biodegradabihty is attempted. Starch and additives have been evaluated ia detail from the perspective of stmcture and compatibiUty with starch (214). 

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