Chapter 2 Polyacetylenes

The polymers which have stimulated the greatest interest are the polyacetylenes, poly-p-phenylene, poly(p-phenylene sulphide), polypyrrole and poly-1,6-heptadiyne. The mechanisms by which they function are not fully understood, and the materials available to date are still inferior, in terms of conductivity, to most metal conductors. If, however, the differences in density are taken into account, the polymers become comparable with some of the moderately conductive metals. Unfortunately, most of these polymers also have other disadvantages such as improcessability, poor mechanical strength, instability of the doped materials, sensitivity to oxygen, poor storage stability leading to a loss in conductivity, and poor stability in the presence of electrolytes. Whilst many industrial companies have been active in their development (including Allied, BSASF, IBM and Rohm and Haas,) they have to date remained as developmental products. For a further discussion see Chapter 31. 

Organic compounds like polyacetylene are another example of this class of intercalation compound, as discussed in Chapter 5. 

This chapter surveys the polymerization of substituted acetylenes focusing on the research during this decade. Monomers and polymers, polymerization catalysts, controlled polymerizations, and functional polyacetylenes are discussed. Readers are encouraged to access other reviews and monographs on the polymerization of substituted acetylenes, and a,cj-diynes. ... 

As described in Chapter 6, Electric Properties of Polymers, there is a general relationship between the delocalization of electrons throughout a polymer chain or network and color so that the incidence of and darkness of color increases as electron delocalization increases. Thus polyethylene is colorless while polyacetylene is black. 

Though conductivity of polyaniline is not as high as that of some other polymers, it is emerging as the material of choice for many applications. It is stable in air and its electronic properties can be easily tailored. It is one of the oldest synthetic polymers, and probably it is the cheapest conducting polymer used in devices. It can be easily fabricated as thin films or patterned surfaces. Polyaniline will never replace the materials which have extremely high conductivity. However, it will be useful for certain specific applications. Andy Monkman has a program to extrude the polymer braids and lay the insulation of the coaxial cables in a single step. The work is supported by a cable company [3], Properties of polyacetylene are discussed in detail in Chapter 2. 

We have discussed the physics and technology of polyacetylene in detail in this chapter. A good understanding of the physics of polymers became possible as a result of the work done on poly acetylene. 

The chemistry of acyclic, synthetic polyacetylenes will be considered in this chapter. Cyclic and naturally occuring polyacetylenes are covered in separate chapters. Although most of the discussion is directed toward conjugated polyynes, reactions of non-conjugated derivatives are included in which interactions between triple bonds play an important role. Earlier work in the area has been reviewed thoroughly and consequently in this chapter attention is directed mainly toward some of the more recent advances. 

Besides processes (1) and (2), the reader should be aware that nucleophilic attacks on alkynes are treated in other chapters of this book, dealing with rearrangements, cyclizations, polyacetylenes, cyclic acetylenes and perhaps others. A number of publications overlap with ours in different ways and at different levels -. They treat individual alkynes or families " , e.g. acetylene, diacetylenes , acetylene dicarboxylic esters haloacetylenes , alkynyl ethers and thioethers > ynamines , fluoro-alkynes ethynyl ketpnes , nitroalkynes , etc. synthetic targets, e.g. pyrazoles , if-l,2,3-triazoles , isothiazoles , indolizines S etc. reagents, e.g. nitrones , lithium aluminium hydride , heterocyclic A -oxides - , azomethine ylids - , tertiary phosphorus compounds , miscellaneous dipolar nucleophiles - , etc. The reader will appreciate that all of these constitute alternate entries into our subject. 

This chapter has provided some examples of the ways in which conjugated polymers can be prepared. While the account is not of course exhaustive, and indeed many extremely important synthetic routes have not been included, such as the formation of polyacetylene by the Durham route,it does serve to illustrate that the range of synthetic techniques vary from the simple to the extremely sophisticated. Electrochemical synthesis is largely in the former classihcation, however, it does have considerable potential in the design of materials for molecular electronics since it will allow patterns to be formed on the electrode surface. With the continuing demand for new materials both for electronic and power distribution needs, it is to be expected that this area will continue to develop in the foreseeable future. 

This chapter is organized as follows the experimental and theoretical techniques are presented briefly in Sections 5.2 and 5.3. In Section 5.4 some materials aspects and concepts are introduced, where rrani -polyacetylene is used as an illustrative example. A series of illustrative examples on surfaces and interfaces... 

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. 

In this chapter, we will focus on cyclic mono- and diacetylenes, as other topics, such as cyclic oligo- and polyacetylenes or dehydroannulenes [2 a], have either been reviewed in detail [1-3] or are covered by the corresponding contributions to this publication. Extremely strained systems which have been detected only by trapping reactions have been reviewed very recently [3 c] and are not included here. 

This chapter presents a broad overview of our work on the synthesis and properties of macrocyclic homoconjugated polyacetylenes. The synthetic methods discovered, invented, developed, and used in this arena, of course, have applicability in the wider field of modem acetylene chemistry, and it is our hope that others will benefit from the findings described in the following sections of this chapter. 

This chapter will focus on some recent developments in the synthesis of polyacetylene itself, (CH) , and of substituted derivatives, (CR) f(CH) [24, 25]. While the great variety of other conductive polymers, including poly(phenylene vinylenes), polythiophenes and polypyrroles, may be thought of as annulated derivatives of polyacetylene [26-28], (Fig. 10-4), their syntheses and properties differ enough to put them outside the scope of this chapter. The reader is referred to a number of reviews covering both these polymers and polyacetylene [15,17, 29]. 

Polyacetylene itself has not found application in light-emitting diodes. rrans-Polyacetylene has a very low quantum yield for emission, being instead an efficient photoconductor. See Chapter 6 in [14]. 

Section II of this chapter will discuss the synthesis and properties of polyacetylene, a linear polyene without a substituent. Section III will deal with the synthesis and properties... 

Substituted polyacetylenes have not been studied for their conduction properties, but rather for different high-performance features. Substituents appear to reduce conjugation by introducing twists in the main chain. Structural data on polyphenylacetylene have been reported by Simionescu and Percec [155] these can be found in the 1986 Handbook [156]. A polymer stnicturally related to polyacetylene, poly( 1,6-hepta-diyne), is briefly dealt with in Section 7.2 of this chapter. 

In this chapter the second moment studies are mainly reviewed for the two typical conjugated polymers Shirakawa-type (S-PA) [20-22,27,30-32] and Naar-mann and Theophilou-type (NT-PA) polyacetylenes [24] and polyparaphenylene [23,28,29]. The characteristic of NT-PA is a high degree of chain orientation attained by mechanical stretching, [33] which provides additional information on tlie polymer chain arrangement how much misorientatioii of the chains is left behind and how much of the amorphous portion exists [34]. From an analysis of the second moment M2... 

For the rest of this chapter we compare the above results with other ENDOR studies of polyacetylene. A spin density much more delocalized than that of the soliton theory was proposed from the studies of unoriented C-enriched cw-rich sample [110,116,117]. The proposed spin density consists of only two kinds of spin densities 0.06 and -0.02, the results being quite different from those obtained in stretched ci s-rich samples. The small magnitude of the proposed spin density of p(0) = 0.06 could result from the fact that the apparent frequency span of the C-enriched system, giving v o+ is much smaller than that of the pristine system. Proposed spin densities were deduced by the assignments of the structures of the observed lineshape to C or proton hyperfine components. Later comparison between pristine and C -enriched systems, however, revealed that the structures of the spectra of C-enriched system resulted from the... 

Features of synthesis, structure, properties, and use of polyacetylenes are considered in this chapter. The catalytic polymerization of acetylene using different catalysts is shown. Plasmachemical synthesis of carbines is considered. The results of studying the structure of polyacetylenes by electron spectroscopy are presented. The results of the research of the surface morphology of polyacetylene are presented. Agency of receiving methods of polyacetylene on its properties is shown. 

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