Poly acetylene s

In 1975, it was discovered that WCk, which is a typical metathesis catalyst, is capable to catalyze the polymerization of phenylacetyl-ene. Subsequently, various substituted acetylenes have been polymerized by this type of catalyst. In 1983, poly(l-(trimethylsilyl)-l-propyne)) was synthesized in the presence of Tads and NbCls (35). The alkyne polymerization has many similarities with ROMP. 

The polymerization of substituted alkynes is postulated to proceed either by the metathesis mechanism or by an insertion mechanism (18). Numerous alkyne derivates have been shown to polymerize in the presence of group V, VI, and VIII transition metal catalysts. 

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Poly-(acetylene)s are widely used in different fields, such as organic light-emitting diodes (OLEDS), solar cells, and lasers.135 Synthesis... 

A major reason for the failure of poly(acetylene)s in the above-mentioned applications is related to their inherent instability versus moisture and oxygen, and their high susceptibility to decomposition/rearrangement in the partially oxidized/doped state. Nevertheless, poly(ene)s stabilized by appropriate ligand systems and/or incorporated into cyclic structures are believed to exhibit similar stabilities to poly(thiophene)s, poly(pyrrole)s, poly(p-phenylene)s, PPV, and so on. In the following, we will outline the basic concepts of poly(ene)s as well as reviewing the structures that have been realized so far. 

With the idea of avoiding the potential bimolecular coupling reaction of the radical centers in the solution-phase chemical oxidation reactions, a photochemical approach was adopted. Diazo compounds 10 and 12 were treated with the Rh catalyst under basic conditions to give the poly(acetylene)s 43 [R and m- /7-(/i-C,9H39)C6H4]C(N2)] of 200000 [8]. While photolysis of the diazo groups proceeded smoothly on neat films at 2 K and broad EPR si-... 

Of the plethora of systems containing conjugated double bonds, poly(acetylene)s, poly(heterocycle)s, and poly(aminoaromatic) compounds are undoubtedly the most popular both in regard to their electrical conductivity and their stability and ease of preparation. Poly(acetylene), poly(pyrrole), and poly(aniline) are the most intensively studied polymers. 

Later in 1974 Japanese scientists published the polymerization of acetylene [12] on the surface of a high concentrated solution of Ziegler-Natta catalyst, receiving also poly(acetylene) films with a metallic lustre. These small film pieces—inspite of their impurities (O 1.0%, Ti + A1 0.5%)—had one remarkable property they were dopable reaching values of up to 2500 S/cm. What was the reason for that unusual behaviour in case of other known poly(acetylene)s, e.g., the cuprene film with a lustre like copper or nickel and was produced in large quantities and sizes ... 

Mechanical stretching can be performed after polymerization, e.g., in noncross-linked polymers. In the case of poly(acetylene)s prepared with aged Ziegler-Natta catalysts [34] stretching increases conductivity from 2500 S/cm to values as high as 10 S/cm. 

Since doped poly(acetylene)s were shown to possess metallic conductivity, this class of organic polymers has been studied intensively. Regardless of the catalyst system used, it is an inherent disadvantage of the washing process which is required to remove the catalyst or residues from the desired polymer preparation. Therefore a method was developed that avoids this pitfall and provides polyene films that form a solid layer on glass surfaces, ceramic plates, tubes, etc. 

The synthesis of polymers from substituted acetylene monomers is directed toward the preparation of substituted, conjugated chains which ameliorate the negative properties of poly(acetylene)s (e.g., sensitivity to air, insolubility, and infusibility) while maintaining the desired electrical properties of acetylene s conjugated backbone alkyl- and aryl substituted polymers result. They are soluble (e.g., in toluene and cyclohexane) and proccessible, but have low conductivities (<0.1 S/cm) compared with the unsubstituted poly(acetylene). 

By 1988, a number of devices such as a MOSFET transistor had been developed by the use of poly(acetylene) (Burroughes et al. 1988), but further advances in the following decade led to field-effect transistors and, most notably, to the exploitation of electroluminescence in polymer devices, mentioned in Friend s 1994 survey but much more fully described in a later, particularly clear paper (Friend et al. 1999). The polymeric light-emitting diodes (LEDs) described here consist in essence of a polymer film between two electrodes, one of them transparent, with careful control of the interfaces between polymer and electrodes (which are coated with appropriate films). PPV is the polymer of choice. 

Fig. 14. Amplitude dependences (y0 is the amplitude of cyclic deformations) of the elastic modulus for frequency a) = 63 s 1 13% dispersion of acetylene carbon black in low- (/) and high-molecular (2) poly(isobutylene)s...

Figure 13 shows the irreversible conversion of a nonconjugated poly (p-phenylene pentadienylene) to a lithiun-doped conjugated derivative which has a semiconducting level of conductivity (0.1 to 1.0 S/cm) (29). Obviously, the neutral conjugated derivative of poly (p-phenylene pentadienylene) can then be reversibly generated from the n-type doped material by electrochemical undoping or by p-type compensation. A very similar synthetic method for the conversion of poly(acetylene-co-1,3-butadiene) to polyacetylene has been reported (30), Figure 14. This synthesis of polyacetylene from a nonconjugated precursor polymer containing isolated CH2 units in an otherwise conjugated chain is to be contrasted with the early approach of Marvel et al (6) in which an all-sp3 carbon chain was employed.

Haloarene derivatives used for coordination polycondensation are primarily represented by halostyrenes and haloarylacetylenes which undergo selfcoupling to poly(arylene vinylene)s [scheme (2)] and poly(aryleneacetylene)s [scheme (3)] respectively, and by dihaloarenes which, mainly in a combination with alkenes or divinylarenes and acetylenes or diacetylenes, undergo crosscoupling to poly(arylene vinylene)s [schemes (4) and (5)] and poly(arylene acetylene)s [schemes (6) and (7)] respectively [2] ... 

In addition to aryl alkynyl coupling reactions involving dihaloarenes and acetylenes or dialkynylarenes which lead to poly(arylene acetylene)s, it is worth noting that these polymers have also been obtained by the Pd(0)-catalysed heteropolycondensation of dialkoxy-substituted dibromoarenes with bis(tribu-tylstannyl)acetylenes [122]. 

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