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Vinyl selectivity

FIGURE 11.5 Diene comonomers for vinyl-selective copolymerizations with propylene. [Pg.307]

Fig. 1 Vinyl end-group content and selectivity in the homopolyethylenes produced with selected metallocenes. Vinyl selectivity has been calculated from the GPC (Mn) and FTIR data. Polymerization conditions T = 80°C, MAO cocatalyst, solvent toluene. Trendlines are to guide the eye. Figure adapted fi-om [168]... Fig. 1 Vinyl end-group content and selectivity in the homopolyethylenes produced with selected metallocenes. Vinyl selectivity has been calculated from the GPC (Mn) and FTIR data. Polymerization conditions T = 80°C, MAO cocatalyst, solvent toluene. Trendlines are to guide the eye. Figure adapted fi-om [168]...
The indenyl-substituted bridged Zr-catalysts (4, 9, 15, 16) exhibit very high vinyl selectivity, which is typically almost 100%. A decrease in the monomer concentration slightly lowers the vinyl selectivity. Intermediate vinyl selectivities have been observed for non-bridged Cp metallocenes, e.g., 1 and 3. The polyethylenes produced with the latter catalyst typically had lower vinyl contents... [Pg.191]

Chain transfer to the monomer is judged to be the major chain transfer mechanism with the indenyl bridged zirconium catalysts. This conclusion is based on the following two findings (1) vinyl selectivity is approximately one unsaturation in each chain, which suggests that chain transfer to MAO is neghgible, and (2) the is independent of ethylene concentration, which rules out p-H eliminatimi. [Pg.193]

The cyclohexadiene derivative 130 was obtained by the co-cyclization of DMAD with strained alkenes such as norbornene catalyzed by 75[63], However, the linear 2 1 adduct 131 of an alkene and DMAD was obtained selectively using bis(maleic anhydride)(norbornene)palladium (124)[64] as a cat-alyst[65], A similar reaction of allyl alcohol with DMAD is catalyzed by the catalyst 123 to give the linear adducts 132 and 133[66], Reaction of a vinyl ether with DMAD gives the cyclopentene derivatives 134 and 135 as 2 I adducts, and a cyclooctadiene derivative, although the selectivity is not high[67]. [Pg.487]

Hydrometallation is catalyzed by Pd. Hydroboration of l-buten-2-methyl-3-yne (197) with catecholborane (198) gives the 1,4-adduct 199 with 84% selectivity. The ratio of Pd to phosphine (1 1.5) is important[l 10]. The vinyl sulfide 201 is prepared by a one-pot reaction of the thioalkyne 200 via a Pd-catalyzed hydroborution-coupling sequence using dppf as a ligand[l 11]. [Pg.495]

First, we consider the experimental aspects of osmometry. The semiperme-able membrane is the basis for an osmotic pressure experiment and is probably its most troublesome feature in practice. The membrane material must display the required selectivity in permeability-passing solvent and retaining solute-but a membrane that works for one system may not work for another. A wide variety of materials have been used as membranes, with cellophane, poly (vinyl alcohol), polyurethanes, and various animal membranes as typical examples. The membrane must be thin enough for the solvent to pass at a reasonable rate, yet sturdy enough to withstand the pressure difference which can be... [Pg.548]

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). [Pg.320]

The metals are impregnated together or separately from soluble species, eg, Na2PdCl4 and HAuCl or acetates (159), and are fixed by drying or precipitation prior to reduction. In some instances sodium or potassium acetate is added as a promoter (160). The reaction of acetic acid, ethylene, and oxygen over these catalysts at ca 180°C and 618—791 kPa (75—100 psig) results in the formation of vinyl acetate with 92—94% selectivity the only other... [Pg.385]

Selection of organic peroxides for various commercial appHcations has been reviewed (21,33,48), particularly for vinyl chloride polymerizations (30). [Pg.228]

The selectivity of pervaporation membranes varies considerably and has a critical effect on the overall separation obtained. The range of results that can be obtained for the same solutions and different membranes is illustrated in Figure 41 for the separation of acetone from water using two types of membrane (89). The figure shows the concentration of acetone in the permeate as a function of the concentration in the feed. The two membranes shown have dramatically different properties. The siUcone mbber membrane removes acetone selectively, whereas the cross-linked poly(vinyl alcohol) (PVA) membrane removes water selectively. This difference occurs because siUcone mbber is hydrophobic and mbbery, thus permeates the acetone preferentially. PVA, on the other hand, is hydrophilic and glassy, thus permeates the small hydrophilic water molecules preferentially. [Pg.86]

Fig. 41. The pervaporation separation of acetone—water mixtures achieved with a water-selective poly(vinyl alcohol) (PVA) membrane and with an acetone-selective siUcone mbber membrane. The PVA membrane is best suited to removing small amounts of water from a concentrated acetone solution, whereas the siUcone mbber membrane is best suited to removing small amounts of acetone from a dilute acetone stream (89). Fig. 41. The pervaporation separation of acetone—water mixtures achieved with a water-selective poly(vinyl alcohol) (PVA) membrane and with an acetone-selective siUcone mbber membrane. The PVA membrane is best suited to removing small amounts of water from a concentrated acetone solution, whereas the siUcone mbber membrane is best suited to removing small amounts of acetone from a dilute acetone stream (89).
The acetone-selective, siUcone mbber membrane is best used to treat dilute acetone feed streams and concentrate most of the acetone in a small volume of permeate. The water-selective, poly(vinyl alcohol) membrane is best used to treat concentrated acetone feed streams containing only a few percent water. Most of the water is then removed and concentrated in the permeate. Both membranes are more selective than distillation, which rehes on the vapor—hquid equiUbrium to achieve a separation. [Pg.87]

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. [Pg.368]

The web materials used to form dmms and cans can be customized to each packaging apphcation. The materials are selected based on the package properties of moisture and humidity resistance, nonstick resistance, or barrier properties required. The adhesives used to bond the phes together include sihcates, poly(vinyl alcohol), and poly(vinyl acetate) (10). Sihcate adhesives are most commonly used in the manufacture of dmm packages. [Pg.519]

Increasingly, plastics are being used as parenteral packaging (qv) materials. Plastics such as poly(vinyl chloride), polyethylene, and polypropylene are employed. However, plastics may contain various additives that could leach into the product, such as plasticizers (qv) and antioxidants. PermeabiUty of plastics to oxygen, carbon dioxide, and water vapor must be tested in the selection of plastic containers. Furthermore, the plastic should withstand sterilization. Flaking of plastic particles should not occur and clarity necessary for inspection should be present. [Pg.234]


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