Shirakawa technique

Polyacetylenes. The first report of the synthesis of a strong, flexible, free-standing film of the simplest conjugated polymer, polyacetylene [26571-64-2] (CH), was made in 1974 (16). The process, known as the Shirakawa technique, involves polymerization of acetylene on a thin-film coating of a heterogeneous Ziegler-Natta initiator system in a glass reactor, as shown in equation 1. 

To the naked eye the material produced by the Shirakawa technique appears to be a film, but electron microscopy reveals a fairly complex... 

When acetylene is polymerized by the Shirakawa technique at low temperature, c. — 70°C, the product film has a yellow-gold appearance, it is an insulator with a conductivity of c. 10 (Qcm) and it has a low free spin density. Diffraction and spectroscopic studies establish that there is regular single-double bond alternation and that the material is predominantly the cis-cisoid homopolymer. However, this material is stable only at low temperature, and when the polymerization is conducted at room temperature a different material with a silvery appearance and a predominantly trans-transoid structure is obtained essentially the same material is produced when the cis polymer is allowed to warm to room temperature. This form of polyacetylene is a semiconductor with conductivity in the to... 

Our samples have been polymerized by the Shirakawa technique at -80 C /8/ and the films floating on the top of the catalyst solution have been used for the investigations. At -80 °C predominantly cis-polyacetylene is pbtained, for conversion into the trans modification the samples have been heated at 190 °C in an Argon atmosphere for 5 minutes. Some characteristic parameters... 

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. 

Grafts. Polyacetylene films were synthesized at -78°C using techniques similar to those developed by Shirakawa and coworkers (11). Reductive doping was carried out in a dry box by immersion of (CH)X films in 1 M sodium naphthalide/THF solutions for 2 minutes. The films were then washed several times with dry, 02-free THF and allowed to stand in fresh THF for approximately 1 hour. The conductivities and compositions of the films were in the range 5-50 S/cm and [CHNaQ O-0.25]x respectively. 

The synthesis of the polyacetylene powder has been known since the late 1950s, when Natta used transition metal derivatives that have since become known as Ziegler-Natta catalysts. The characterization of this powder was difficult until Shirakawa and coworkers [18] succeeded in synthesizing lustrous, silvery, polycrystalline films of polyacetylene (which has become known as Shirakawa polyacetylene) and in developing techniques for controlling the content of cis and trans isomers ... 

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