Shirakawa catalyst

One of the most interesting alternatives to the Shirakawa catalyst has been the systems disclosed by Luttinger 22-23) and later elaborated by Lieser et al. 24). The tris(2-cyanoethyl)phosphine complex of nickel chloride reacts with sodium boro-hydride to produce a catalyst system capable of polymerizing acetylene in solutions in either alcohol or, quite remarkably, water. A more efficient catalyst is obtained by replacing the nickel complex with cobalt nitrate. Interest in Luttinger polyacetylene seems to have waned in the last few years. 

Several attempts to induce orientation by mechanical treatment have been reviewed 6). Trans-polyacetylene is not easily drawn but the m-rich material can be drawn to a draw ratio of above 3, with an increase in density to about 70% of the close-packed value. More recently Lugli et al. 377) reported a version of Shirakawa polyacetylene which can be drawn to a draw ratio of up to 8. The initial polymer is a m-rich material produced on a Ti-based catalyst of undisclosed composition and having an initial density of 0.9 g cm-3. On stretching, the density rises to 1.1 g cm-3 and optical and ir measurements show very high levels of dichroism. The (110) X-ray diffraction peak showed an azimuthal width of 11°. The unoriented material yields at 50 MPa while the oriented film breaks at a stress of 150 MPa. The oriented material, when iodine-doped, was 10 times as conductive (2000 S cm-1) as the unstretched film. By drawing polyacetylene as polymerized from solution in silicone oil, Basescu et al.15,16) were able to induce very high levels of orientation and a room temperature conductivity, after doping with iodine, of up to 1.5 x 10s S cm-1. 

Instead of bemoaning the error, Shirakawa decided to learn more about this fascinating new version of an old familiar polymer, polyacetylene. He soon discovered that the silvery film consisted of the trans form of polyacetylene and that a comparable copper-colored film could he produced with large quantities of catalyst at different temperatures. The copper-colored film was found to consist of the cis form of the polymer. 

The cyclohomopolymerisation of 1,6-heptadiyne by using Shirakawa [85] and related [86] catalysts is a representative insertion polymerisation of acetylenic monomers with Ziegler-Natta catalysts ... 

The most commonly used method to synthesize the PA is the Shirakawa method. In this method a smooth surface wetted by the Ziegler-Natta catalyst is exposed to the acetylene gas. A film of PA (generally c-PA) is produced on the smooth surface. The c-PA is converted to the f-PA by heating. The process of doping also converts the c-PA to the r-PA. 

Suspensions of polyacetylene were prepared as burrs or fibers (46) by using a vanadium catalyst. When the solvent was removed, films of polyacetylene were formed with densities greater than that prepared by the Shirakawa method. These suspensions were mixed with various fillers to yield composite materials. Coatings were prepared by similar techniques. Blends of polypyrrole, polyacetylene, and phthalocyanines with thermoplastics were prepared (47) by using the compounding techniques typically used to disperse colorants and stabilizers in conventional thermoplastics. Materials with useful antistatic properties were obtained with conductivities from 10" to 10" S/cm. The blends were transparent and had colors characteristic of the conducting polymer. For example, plaques containing frans-polyacetylene had the characteristic violet color exhibited by thin films of solid trans-polyacetylene. 

Shirakawa, E., Hiyama, T. The palladium-iminophosphine catalyst for the reactions of organostannanes. J. Organomet. Chem. 1999, 576, 169-178. 

Shirakawa and Hiyama found that transition metals such as palladium and nickel are efficient catalysts for a series of carbostannylations, the first one of which is the palladium-catalyzed alkynylstannylation of alkynes described in the following section. Both palladium and nickel catalyze the allylstannylation of alkynes (Schemes 5.7.6 and 5.7.7). In contrast to the methods using a radical initiator or a Lewis acid catalyst, these additions proceed with. yyn-selectivity. Both catalysts complement each other in terms of the range of alkynes that can be employed palladium prefers electron-deficient alkynes. 

Hattori, T. Kijima, M. Shirakawa, H. Oxidative polycondensation of acetylene by iodine in the presence of palladium-copper catalyst. Synth. Met. 1997, 84, 357-358. 

A 50-mL aliquot of the original Shirakawa catalyst was diluted with 100 ml of freshly distilled toluene, and a 0.9597-gram sample of polypropylene membrane, taken from the same lot as before, was soaked in this solution. The sample weighed 1.1266 grams after catalyst pickup, or an increase in weight of 17.4%. 

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