Catalysis solution polymerization

Figure 6.2 Structure of a CGC useful for solution polymerization of ethylene (JC Stevens, IP Int l Congress on Catalysts 40 Anniv., Studies in Surface Science and Catalysis, Vol. 101, p 11,1996 see also K Swogger, International Conference on Polyolefins, Society of Plastics Engineers, Houston, TX, February 25-28,2007).

The kinetics of solution polymerizations involving CCT are not substantially different from bulk polymerizations. An initial report that toluene as a solvent led to reduced catalysis rate336 seems to be unfounded.124... 

Inspection of Table 2, entries 1-4, shows that optimum conversion and polyester molecular weight from 1 were at 70 °C. HiC activity dropped precipitously for polymerizations conducted at 80 °C. These results agree with those described above for condensation polymerizations. By performing poly-(e-caprolactone) in toluene instead of in bulk at 70 "C, Mi increased from 16 000 to 24 900 and Afw/Mi decreased from 3.1 to 1.7. An increase in Mi is expected for solution polymerizations since the solvent decreases the viscosity of the reaction medium, thereby easing diffusion constraints between substrates and the enzyme. However, the decrease in polydispersity for the solution polymerizations is less easily explained. One possibility is that transesterification reactions leading to broader polydispersity occur more rapidly for reactions conducted in bulk. HiC catalysis of a>-pentadecalactone (2) polymerization in... 

Following World War II the focus on SBR turned to development of specific products demonstrating improvement in selected properties over natural rubber as well as the original SBR. The first such development was the emulsion polymerization of styrene and butadiene at low temperature in the presence of a redox catalyst system. The product from this type of process represented a marked improvement over natural rubber in tread stocks for passenger car tires. Subsequently, application of or-ganolithium catalysis permitted development of solution-polymerized SBRs that offered improvements over emulsion SBR in curing rate... 

Other solubilization and partitioning phenomena are important, both within the context of microemulsions and in the absence of added immiscible solvent. In regular micellar solutions, micelles promote the solubility of many compounds otherwise insoluble in water. The amount of chemical component solubilized in a micellar solution will, typically, be much smaller than can be accommodated in microemulsion fonnation, such as when only a few molecules per micelle are solubilized. Such limited solubilization is nevertheless quite useful. The incoriDoration of minor quantities of pyrene and related optical probes into micelles are a key to the use of fluorescence depolarization in quantifying micellar aggregation numbers and micellar microviscosities [48]. Micellar solubilization makes it possible to measure acid-base or electrochemical properties of compounds otherwise insoluble in aqueous solution. Micellar solubilization facilitates micellar catalysis (see section C2.3.10) and emulsion polymerization (see section C2.3.12). On the other hand, there are untoward effects of micellar solubilization in practical applications of surfactants. Wlren one has a multiphase... 

Since the principal hazard of contamination of acrolein is base-catalyzed polymerization, a "buffer" solution to shortstop such a polymerization is often employed for emergency addition to a reacting tank. A typical composition of this solution is 78% acetic acid, 15% water, and 7% hydroquinone. The acetic acid is the primary active ingredient. Water is added to depress the freezing point and to increase the solubiUty of hydroquinone. Hydroquinone (HQ) prevents free-radical polymerization. Such polymerization is not expected to be a safety hazard, but there is no reason to exclude HQ from the formulation. Sodium acetate may be included as well to stop polymerization by very strong acids. There is, however, a temperature rise when it is added to acrolein due to catalysis of the acetic acid-acrolein addition reaction. 

Copolymers of diallyl dimethyl ammonium chloride [7398-69-8] with acrylamide have been used in electroconductive coatings (155). Copolymers with acrylamide made in activated aqueous persulfate solution have flocculating activity increasing with molecular weight (156). DADM ammonium chloride can be grafted with cellulose from concentrated aqueous solution catalysis is by ammonium persulfate (157). Diallyl didodecylammonium bromide [96499-24-0] has been used for preparation of polymerized vesicles (158). 

These siUca-supported catalysts demonstrate the close connections between catalysis in solutions and catalysis on surfaces, but they are not industrial catalysts. However, siUca is used as a support for chromium complexes, formed either from chromocene or chromium salts, that are industrial catalysts for polymerization of a-olefins (64,65). Supported chromium complex catalysts are used on an enormous scale in the manufacture of linear polyethylene in the Unipol and Phillips processes (see Olefin polymers). The exact stmctures of the surface species are still not known, but it is evident that there is a close analogy linking soluble and supported metal complex catalysts for olefin polymerization. 

The occurrence of stereospecific polymerization in solution has been explained by the stetic restrictions of ligands bonded to the metal center. For example, the following stmcture has been postulated as an intermediate in solution catalysis (68) ... 

Indole itself forms a dimer or a trimer, depending on experimental conditions the dimer hydrochloride is formed in aprotic solvents with dry HCl, whereas aqueous media lead to dimer or trimer, or both. It was Schmitz-DuMont and his collaborators who beautifully cleared up the experimental confusion and discovered the simple fact that in aqueous acid the composition of the product is dictated by the relative solubilities of the dimer and trimer hydrochlorides/ -This, of course, established the very important point that there is an equilibrium in solution among indole, the dimer, the trimer, and their salts. It was furthermore demonstrated that the polymerization mechanism involves acid catalysis and that in dilute solution the rate of reaction is dependent on the concentration of acid. 

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

The problem of transport of molecules through swollen gels is of general interest. It not only pertains to catalysis, but also to the field of chromatographic separations over polymeric stationary phases, where the partition of a solute between the mobile phase (liquid phase) and a swollen polymeric stationary phase (gel phase) is a process of the utmost importance. As with all the chemical and physicochemical processes, the thermodynamic and the kinetic aspect must be distinguished also in partition between phases. 

Polystyrene is unusual among commodity polymers in that we can prepare it in a variety of forms by a diversity of polymerization methods in several types of reaction vessel. j Polystyrene may be atactic, isotactic, or syndiotactic. Polymerization methods include free radical, cationic, anionic, and coordination catalysis. Manufacturing processes include bulk, solution, suspension, and emulsion polymerization. We manufacture random copolymers ... 

Crown ethers attached to insoluble polymeric substrates (see the following discussion for examples) have been used as phase transfer catalysts for liquid/liquid systems. In using such systems, the catalyst forms a third insoluble phase the procedure being referred to as triphase catalysis (Regen, 1979). This arrangement has the advantage that, on completion of the reaction, the catalyst may be readily separated from the reaction solution and recycled (Montanari, Landini Rolla, 1982). As... 

These results indicate that FI catalysts favor the isomer A structure, and that they can be present as a mixture of isomers A and B in solution. It is important to note that an FI catalyst generally exhibits fluxional character in solution, which can result in unique polymerization catalysis. 

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