Butadiene-rich phase

Tie lines of the system can be generated from the equilibrium compositions for each run and selectivities computed. The results of measurements obtained for the 5% by volume of ammonia/ethylene are represented in the binodal diagram in Fig. 3. Butene is represented as the distributed component between the solvent phase and the butadiene-rich phase. The ammonia-solvent gas mixture was considered to behave as a pseudo-solvent of fixed composition. The ratio of the integrated peaks for butene(i) and butadiene(j) was used to compute the selectivity, B (beta), defined on a solvent-free basis, as ... 

Carboxylated polybutadiene ionomers, which are close relatives of the polyethylene ionomers described above, have an essentially polybutadiene backbone that contains some acrylonitrile and styrene to adjust its flexibility and toughness, and, in addition, up to 6% by weight of acrylic or methacrylic acid. Like the polyethylene ionomers, they are usually made by direct copolymerization with the carboxylic acid monomer using, however, emulsion methods. Typically the monomers are slurried in water with sodium dodecylbenzene sulfonate as the emulsifier and potassium persulfate as the free-radical initiator. The tendency of the carboxyhc add monomer to dissolve in the aqueous phase instead of remaining in the butadiene-rich phase is suppressed by making the aqueous phase acidic so that the monomer remains in the nonionized form. 

Figure 17.6a is a TEM image of an ultrathin section of the HIPS sample that had been stained with osmium tetroxide vapor [64]. The aim of such staining was to render the internal stracture of the HIPS visible by selectively depositing a heavy-metal component in the butadiene-rich phase (or in the component with C=C unsaturated bonds). The image showed the typical salami stmcture of the sample, while the butadiene-rich phase and the crazes appeared as dark areas. This imaging was especially important because it provided information as to how the crazes evolved, wandered, and were eventually stopped by the presence of the salami particles. 

The introduction of rubber particles increases the fracture energy of the networks at room temperature, but also decreases the temperature of the ductile-brittle transition (Van der Sanden and Meijer, 1993). This ductile-brittle transition is strongly dependent on the nature (and Tg) of the rubber-rich phase and the amount of rubber dissolved in the matrix. The lowest ductile-brittle transition is obtained with butadiene-based copolymers (Tg — 80°C), compared with butylacrylate copolymers (Tg —40°C). 

For epoxy networks modified by liquid reactive rubbers, it is not so easy to discuss these parameters separately, because they are interdependent. For example, an increase in the acrylonitrile content of the carboxy-termi-nated butadiene acrylonitrile rubber (CTBN) induces a size reduction of the rubbery domains but also a higher miscibility with the epoxy-rich phase, leading to a higher amount remaining dissolved in the matrix at the end of cure (Chapter 8). It is not possible to separate the influence of these two effects on toughness. 

The separation of the liquid components in the presence of a supercritical solvent occurs much as it does in liquid extraction with the entrainer, ammonia, concentrating in the liquid to increase the relative volatility of the butene to butadiene. The butadiene migrates to the ammonia-rich phase while the solvent gas phase or "vapor" will contain the butene. 

For propylene rich streaa j undesired propyne/propadiene are presently removed by a liquid phase hydrofining process over supported Pd [2] bimetallic Pd [51 and proinoted CU/AI3O3 catalysts [6 7]. For butene and butadiene rich streams processes are carried out in the liquid phase (XFP process) over supported [2] and bimetallic Pd [8] as well as in the gas phase (DOW KLP process) over bimetallic Cu/Y Al203 [6/7 9] and Pd/AI O [10] Catalysts. The... 

The polystyrene blocks typically have block weights of about 20 000 whilst the polydiene blocks are in the range 35 OOO-ISO 000. In this range the product at room temperature behaves very much like a reinforced vulcanized rubber. It is also observed, by electron microscopy, that a two-phase system exists in which polystyrene-rich spherical domains are embedded in a continuous phase poly-butadiene-rich rubbery matrix (Fig. 17.2). 

Figure 2 The ternary phase diagram for mixtures of styrene/polystyrene/polybutadiene (S/PS/PB). If styrene is polymerized in the presence of poly butadiene, phase separation takes place. Initially, at A, droplets of polystyrene rich phase form within a polybutadiene rich phase. Between B and C the mixture will phase invert and by D the continuous phase will be polystyrene...

Fluorinated alkyl cyanides, such as trifluoroacetonitrile, pentafluoropropionitrile, per-fluorobutyronitrile and chlorodifluoroacetonitrile, react with butadiene in the gas phase at 350-400 °C to afford pyridines in high yields (equation 82)72. The push-pull diene 150 and electron-rich cyanides (acetonitrile or acrylonitrile) furnish pyridines (equation 83)73. 

The extract is then flashed to liberate, the dissolved olefins and. after recompression, to return them to the extractive distillation step. The liquid fraction rich in butadiene and acetylenic compounds is preheated and sent to a regeneration column with 20 trays operating at about 0.2.10 Pa, at 90°C at the top and 150°C at the bottom. The solvent drawn off is recycled, possibly after purification if required. The distillate is partly condensed. The liquid fraction sei es as a reflux, and that in the gas phase is recompressed and partly returned to the absorption step. The crude butadiene remaining is rid of methyiacetylene and heavier compounds in two simple distillation columns, with about 40 and 110 trays respectively, in the presence of r-butylpyrocatechol. 

The separate phases will be rich in one component but may have the other present as a minor component. In order to control compatibility the elastomer may have reactive end groups to enhance interfacial adhesion. A common example in epoxy-resin technology is the carboxy-terminated butadiene-acrylonitrile copolymer (CTBN). The structure is shown in Scheme 1.47. In this resin the solubility in the epoxy resin is conferred by the acrylonitrile group, and an increase in the fraction present decreases the upper critical solution temperature, with 26% acrylonitrile conferring total miscibility of CTBN with a DGEBA-based epoxy resin (Pascault et al, 2002). 

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