Ziegler solution-soluble

Most catalysts for solution processes are either completely soluble or pseudo-homogeneous all their catalyst components are introduced into the reactor as Hquids but produce soHd catalysts when combined. The early Du Pont process employed a three-component catalyst consisting of titanium tetrachloride, vanadium oxytrichloride, and triisobutjlalurninum (80,81), whereas Dow used a mixture of titanium tetrachloride and triisobutylalurninum modified with ammonia (86,87). Because processes are intrinsically suitable for the use of soluble catalysts, they were the first to accommodate highly active metallocene catalysts. Other suitable catalyst systems include heterogeneous catalysts (such as chromium-based catalysts) as well as supported and unsupported Ziegler catalysts (88—90). 

In the early 1990s, solution processes acquired new importance because of their shorter residence times and abiUty to accommodate metallocene catalysts. Many heterogeneous multicenter Ziegler catalysts produce superior LLDPE resins with a better branching uniformity if the catalyst residence time in a reactor is short. Solution processes usually operate at residence times of around 5—10 min or less and are ideal for this catalyst behavior. Solution processes, both in heavy solvents and in the polymer melt, are inherently suitable to accommodate soluble metallocene catalysts (52). For this reason, these processes were the first to employ metallocene catalysts for LLDPE and VLDPE manufacture. 

R. Schonwitz and H. Ziegler, Exudation of water soluble vitamins and some carbohydrates by intact roots of maize seedlings Zea mays L.) into a mineral nutrient solution. Z. Planzenphysiol. 107 1 (1982). 

Initially alkynes were polymerised by trial and error with the use of Ziegler type recipes and the mechanism for these reactions may well be an insertion type mechanism. Undefined metathesis catalysts of ETM complexes were known to give poly-acetylene in their reaction with alkynes (acetylene) [45] and metallacycles were proposed as intermediates. Since the introduction of well-defined catalysts far better results have been obtained. The mechanism for this reaction is shown in Figure 16.24 [46], The conductive polymers obtained are soluble materials that can be treated and deposited as solutions on a surface. 

Homogeneous Ziegler-Natta catalysts of the classic type, capable of olefin polymerisation, are usually derived from reactions of a hydrocarbon soluble transition metal compound with an alkylmetal compound in a hydrocarbon solution (heptane, hexane, toluene). However, the polymer formed in the presence of such soluble Ziegler-Natta catalysts is very often precipitated during polymerisation. 

Solution polymerization. Solution polymerization involves polymerization of a monomer in a solvent in which both the monomer (reactant) and polymer (product) are soluble. Monomers are polymerized in a solution that can be homogeneous or heterogeneous. Many free radical polymerizations are conducted in solution. Ionic polymerizations are almost exclusively solution processes along with many Ziegler-Natta polymerizations. Important water-soluble polymers that can be prepared in aqueous solution include poly(acrylic acid), polyacrylamide, poly(vinyl alcohol), and poly(iV-vinylpyrrolidinone). Poly(methyl methacrylate), polystyrene, polybutadiene, poly(vinyl chloride), and poly(vinylidene fluoride) can be polymerized in organic solvents. 

Manufacture Olefin copolymer VI improvers are produced by solution polymerization of ethylene and propylene catalyzed by soluble Ziegler-Natta catalysts. The most commonly used catalysts are an aluminium alkyl halide with a soluble... 

Polyacetylene (PA), the simplest linear conjugated polymer, has been actively studied for two main reasons. First, the discovery of the direct synthesis method of PA films on the surface of a Ziegler-Natta catalyst solution [1]. Second, the discovery of a large increase in electronic conductivity, due to a synthetic metal by doping with small quantities of electron-attracting species such as iodine, AsFs, etc., or with an electron donor such as sodium. However, because of its high reactivity and poor solubility, it is difficult to obtain the experimental structural data of PA. 

T. Ito, H. Shirakawa, and S. Ikeda. Simultaneous polymerization and formation of polyacetylene film on the surface of concentrated soluble ziegler-type catalyst solution. J. Polym. Sc. Polym. Chem. Edition, 12(1) 11, 1974. 

At the same time, in his lab in Tokyo, Hideki Shirakawa was applying Ziegler-Natta polymerization to the simplest conceivable monomer - acetylene, C2H2. By a fortuitous error he discovered the effect of using 1000 x the usual concentration of a particularly soluble organometalhc catalyst. When he bubbled acetylene gas through the solution, a shiny, silvery film was deposited on the walls of the tube. The morphology of these films... 

Schwartz, S. E. and W. H. White (1981) Solubility equilibria of the nitrogen oxides and oxyacids in dilute aqueous solution. In Advances in environmental sciences and engineering. Vol. 4 (Eds. X R. Pfafflin and E. N. Ziegler), Gordon and Breach Science Publishers, New York, pp. 1 -45... 

Variable-temperature n.m.r. studies of the soluble Ziegler-Natta catalyst TiClMe(7T-C5H5)2 plus aluminium trimethyl in benzene solution suggest equilibrium between two adduct species, (27) and (28). Temperature variation of e.s.r. spectral line-widths indicates some dynamic process in... 

The Ziegler-Natta catalysts can be sub-divided into two groups (1) heterogeneous insoluble catalysts, and (2) homogeneous, or soluble ones. At times, however, it is difficult to distinguish between the two. For instance, it may be hard to determine whether a particular catalyst is truly in solution or merely in a form of a very fine colloidal suspension (and in fact heterogeneous). 

The structure of the soluble Ziegler catalysts from Cp2TiCl2 and (C2H5)3A1 can be explained. If both components are mixed together in heptane at temperatures of up to TO C, then a dark blue solution is produced... 

Ziegler-Natta catalysts are formed by certain combinations of a metal alkyl and a transition metal compound. Although the catalytically active product is usually insoluble in hydrocarbon solvents, soluble catalysts occasionally result. In the latter example, growth of polymer occurs in solution. In heterogeneous catalysis, growth originates on the surface of the precipitate. All... 

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