Polyacetylene-Related Polymers

As discussed earlier, substitution onto the polyacetylene chain invariably has a deleterious effect on dopability and conduction properties. At the same time the stability tends to improve. Masuda et al.583) studied a large range of substituted polyacetylenes and found that stability increased with the number and bulkiness of the substituents, so that the polymers of aromatic disubstituted acetylenes were very stable, showing no reaction with air after 20 h at 160 °C. Unfortunately, none of these polymers is conducting. Deitz et al.584) studied copolymers of acetylene and phenylacetylene they found that poly(phenylacetylene) degrades even more rapidly than does polyacetylene and that the behaviour of copolymers is intermediate. Encapsulation of the iodine-doped polymers had little effect on the degradation, which is presumably at least in part due to iodination of the chain. 

Pochan et al. 585) have studied poly(l,6-heptadiyne), a polyacetylene analogue, which forms dense continuous films. They find oxygen doping follwed by degradation in a manner similar to polyacetylene, except that the rate of degradation is much larger. 

Aldissi 586) has reviewed the stability of block copolymers of acetylene and other non-conducting blocks. The copolymers are somewhat more stable than polyacetylene but the effect is small. 

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Polyacetylene contains conjugated double bonds in a linear structure [51-54], which leads to special electrical conductivity properties. For this reason, polyacetylene and some other related polymers have applications in the optical and electronic industries. Pojyacetylene synthesized at relatively low temperature seems to have a cis-conformation, with two possible cis- forms indicated as c/s-transoid, and frans-cisoid, as shown below ... 

Fifty-nine references on the application of Raman spectroscopy to polymers are cited in a recent popular book on applications of Raman (139). Polyacetylene and related polymers are being widely investigated at this time (140-143). 

For more details on helical polyacetylenes and related polymers, Yashima et al. is an excellent review article. 

This chapter will consider in detail only PHCs and in particular pyrrole- and thiophene-based systems. This limitation implies that other important classes of polyconjugated polymers, such as polyacetylene, polyaiylenes, polyanilines, and related polymers, will not be treated. 

Optical properties are related to both the degree of crystallinity and the actual polymer structure. Most polymers do not possess color site units, so are colorless and transparent. But, some phenolic resins and polyacetylenes are colored, translucent, or opaque. Polymers that are transparent to visible light may be colored by the addition of colorants, and some become opaque as a result of the presence of additives such as fillers, stabilizers, moisture, and gases. 

Solitons are considered to be important defect states in these conjugated polymers (see Fig. 6.48). It has however been shown that correlation energy is the more important factor in giving rise to the energy gap in (CH) (Soos Ramasesha, 1983). Other polymers related to polyacetylene are polythiophene, polypyrrole, poly-phenylenesulphide, and polyparaphenylene (Section 3.3). Extensive measurements on doped polyacetylenes have been reported in the last five years and these materials, unlike other conducting polymers such as (SN), seem to have good technological potential. 

Black polymers, such as polyacetylene, absorb all visible light, but opaque polymers scatter the incident light. As shown by Lord Raleigh, the turbidity r is related to the scattered light per unit volume, integrated over all angles. 

The possible involvement of oxygen in cis-trans isomerisation of polyacetylene and the related question of whether cis- and tram-polymers oxidize at different rates... 

As explained in the introduction, the polysilanes (and related polygermanes and poly-stannanes) are different from all other high polymers, in that they exhibit sigma-electron delocalization. This phenomenon leads to special physical properties strong electronic absorption, conductivity, photoconductivity, photosensitivity, and so on, which are crucial for many of the technological applications of polysilanes. Other polymers, such as polyacetylene and polythiophene, display electron delocalization, but in these materials the delocalization involves pi-electrons. 

Some conducting polymers with a conjugated polyvinyl structure, such as polyacetylene and poly(phenylacetylene), seem likely to be energetic enough, and reactive enough, to give trouble undoped, if they actually have the supposed structure [7]. See Ethylene, Butadiene, Styrene See related NON-METAL PERCHLORATES... 

The second key factor determining permeability in polymers is the sorption coefficient. The data in Figure 2.18 show that sorption coefficients for a particular gas are relatively constant within a single family of related materials. In fact, sorption coefficients of gases in polymers are relatively constant for a wide range of chemically different polymers. Figure 2.25 plots sorption and diffusion coefficients of methane in Tanaka s fluorinated polyimides [23], carboxylated polyvinyl trimethylsiloxane [37] and substituted polyacetylenes [38], all amorphous glassy polymers, and a variety of substituted siloxanes [39], all rubbers. The diffusion... 

The search for new organic metals and superconductors has attracted a great deal of attention in synthetic chemistry and material science since the discovery of high electrical conductivity in conjugated polymers such as polyacetylene [1], Lots of theoretical studies have been carried out in order to understand the mechanism of conductivity and superconductivity in the conjugated polymers and related... 

In the case of a conjugated polymer like polyacetylene, as shown in Figs. 1.8(a) and 1.8(b), the situation with respect to rotation about the nominally single bonds is very different it is controlled by the electronic structure of the backbone bonds rather than by steric hindrance. As will become clear later, when this type of polymer is discussed in relation to conduction, the partial... 

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