Polyacetylene polymeric systems

The oxidation and/or reduction reactions yield polymeric systems having an extended Jt-electron system along the chain. Doping to the conducting state, in the instance of polyacetylene by exposnre to iodine vapor (p-doping, oxidizing). 

In this chapter, we focus on the effect of fluorine as a substituent in a simple polymeric system, polyacetylene. Polyacetylene, of course, has several potentially practical uses because of its conducting and optoelectronic properties (15) and we are interested in studying how F substitution might influence these properties. Our model systems are butadiene and hexatriene, and we discuss both partially fluorinated and perfluorinated materials. Because we discovered that CF - HC hydrogen bonding is important in these systems, we also present results on the nature of the intramolecular hydrogen bond between the CF and OH groups in alcohols and enols. Related results on intramolecular coordination of alkali metals to C-F bonds in fluoroenolates are briefly described. 

On the other hand, orientation is one of the most important factors to enhance the conductivity of one dimensional pi-conjugated polymers like polyacetylene. Several attempts were made to obtain an oriented polyacetylene [3-5]. Akagi and Shirakawa applied magnetic force into a polymerization system consisting of nematic liquid crystals and obtained a highly oriented polyacetylene. Kahlert and Leising synthesized an oriented polyacetylene film by pyrolyzing prepolymers. Ozaki polymerized acetylene on the surface of benzene crystals and prepared an oriented polyacetylene. 

For the ECPs with degenerated ground state, solitons are responsible for the charge transport. Such a polymeric system is polyacetylene. The major problem on the preparation of polyacetylene/Cgjj nanocomposite is the insolubility of polyacetylene. This has led to the discovery of soluble polyacetylene derivatives such as poly(o-trimethylsilylphenylacetylene) (PTMSiPA) [28]. Small amoimts of doping in PTMSiPA is found to enhance the photoconductivity of pristine PTMSiPA [29]. 

The discovery of highly conducting polyacetylene [1] led to research directed toward the study and discovery of new conducting polymeric systems. Thereafter, highly conducting polymers, such as polyphenylenes, polypyrrols, polythiophenes, etc., have been synthesized and extensively studied [2]. 

Our initial objective was to prepare organic polymeric systems which may be modified to electrically conducting materials. The approach was to obtain the butadiyne polymer in a thin film form by taking advantage of the synthetic procedure, characterization techniques and struc re-property insight that have been developed for polyacetylene. The formation of a partially crosslinked polyvinylene system that may reduce or eliminate the requirement of charge carrier transfer by intermolecular chain contact was envisioned (Eq. 2). 

Grubbs has shown that the metathesis of cyclooctatetraene derivatives yielded conducting polyacetylenes although the polymerization system was not living i.e. the polydispersity was not close to 1, and side-reactions have destroyed the initiating chain after the polymer was formed... 

Conjugated polymers and polymeric systems like polydiacetylene, polyacetylene, poly(arylene vinylene), polythiophene, polyaniline, polyimides, and polyesters have been widely studied for their third-order susceptibility. " In addition to pure polymeric systems, investigations of third-order nonU-neatity have also been carried out on small molecules, polymer-doped systems, hybrid inorganic-organic systems, and organometallic complexes. ... 

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. 

Much effort has been expended toward the improvement of the properties of polyacetylenes made by the direct polymerization of acetylene. Variation of the type of initiator systems (17—19), annealing or aging of the catalyst (20,21), and stretch orientation of the films (22,23) has resulted in increases in conductivity and improvement in the oxidative stabiHty of the material. The improvement in properties is likely the result of a polymer with fewer defects. 

C yields a polymer with 90% cis content polymerization at 100°C yields a polymer with >90% trans content. Polyacetylene, doped with an oxidant or a reductant, showed promise as a polymeric semiconductor [Chien, 1984], That promise was not realized because of the oxidative instability of polyacetylene and emergence of cheaper and more stable polymer systems (Sec. 2-14j). Various substituted acetylenes such as phenylacetylene have also been studied [Kanki et al., 2002 Misumi et al., 2000],... 

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. 

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