PAC polyacetylene

Method of synthesis the most common method of synthesis is ring opening metathesis polymerization of molecules such as c clooctatetraene simple method of synthesis of cis isomer involves blowing acetylene onto the stationary surface of Ziegler catalyst  

Catalyst - Zigler-Natta Pd(OAc)2 Huber, J Mecking, S, Angew. Chem. Int. Ed., 45, 6314-17,2006. 

Crystallinity % 80 Saxena, V Malhotra, B D, Handbook of polymers in Elecronics, Ed. Malhotra, B D, Rapra, 2002. 

Cis content % depends on polymerization temperature c/s, which is insulator-like state, can be converted to trans by heating Skanderi, Z Djebaili, A Bouzaher, Y Belloum, M Abadie, M J M, Composites, Part A, 36,497-501, 2005. 

Chain conformation - helix /tkagi, K Mori, T, Chem. Record, 8, 395-406,2008. 

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For a long time there was no consensus of opinion about the morphology of ICPs. On the basis of scanning electron micrographs, some research groups favored a fibrillar structure for PAc (polyacetylene) produced by the Shirakawa method [15]. This would, it was thought, be an explanation for an anisotropy of electrical conductivity that was observed following orientation of the material [26]. 

Fig. 1. (a) Comparison of normalised electrical conductivity of individual MWCNTs (Langer 96 [17], Ebbesen [18]) and bundles of MWCNTs (Langer 94 [19], Song [20]). (b) Temperature dependence of resistivity of different forms (ropes and mats) of SWCNTs [21], and chemically doped conducting polymers, PAc (FeClj-doped polyacetylene [22]) and PAni (camphor sulfonic acid-doped polyaniline [2. ]) [24]. 

The earliest band theory calculations for conjugated polymers were focussed on rrans-polyacetylene (t-PAc). It was the first system in which metallic levels of electrical conductivity were observed (Shirakawa et al., 1977) and has by far the simplest molecular structure of this class of polymers. There are two possible structures, either ... 

The question of whether the bond lengths were equal or alternated in an infinite f-PAc chain was first answered satisfactorily using a Huckel model nearly twenty years before the discovery of metallic behaviour in PAc (Longuet-Higgins and Salem, 1959). This work was carried out at a time when the Huckel model was being used to model the evolution of the optical spectra of the polyenes, i.e. polyacetylene oligomers, as the length of the molecules increased. 

The report of the doping of polyacetylene (PAc) films to produce metallic levels of conductivity by Shirakawa et al. (1977) sparked the interest in electrically conductive polymers that has continued until today. While it was not the first example of a conductive polymer, the increase in conductivity, by a factor greater than 107, observed on exposing films of trans-PAc to arsenic pentafluoride and iodine, was dramatic, see Fig. 9.1. The impact of this result was immediate, and created an upsurge of interest in conjugated polymers and the possibility of rendering them conductive. 

Some of the innovative materials contain PAC in a highly dispersed heterogeneous distribution. Others are homogeneous and soluble. All of them can be processed by conventional techniques such as melt and blow extrusion, fiber spinning, film casting or spin coating. And some of them even provide the necessary matrix stabilization for turning polyacetylene into a useful material. 

When PVAPAC films, optimized with respect to conjugation length distribution and PAC concentration, are stretched in a controlled manner they turn into highly dichroic transparent neutral grey POLPAC filters (Fig. 1.10). The absence of coloration is indicative of an exceptionally highly ordered PAC state in these novel all polymer broadband polarizers based on polyacetylene (POLPAC ). 

By contrast, the ECP must have conjugated rigid-rod macromolecules. Several such polymers show high electrical conductivity (usually after doping), viz. polyacetylene (PAc), polyaniline (PANI), polypyrrole (PPy), polyparaphenylenes (PPP), or poly-3-octyl thiophene (POT). The resins are expensive, difficult to process, brittle and affected by ambient moisture, thus blending is desirable. For uniaxially stretched fibers the percolation threshold is 1.8 vol%, hence low concentration of ECP (usually 5-6 vol%) provides sufficient phase co-continuity to ascertain conductivity similar to that of copper wires (see Table 1.79). 

It is also interesting to note the situation shown in Figure 11.117(b). The pure PAni displays a marked conductivity maximum, whereas the 47% sample shows only a weak maximum and the 20% sample shows none at all. Above room temperature the first two samples—both the pure PAni and the 47% PAni blend—behave like metals in a fashion also observed in numerous highly conductive polyacetylenes. Thus in this respect there is no difference between these materials (PAni, PAni blend and PAc). 

Figure 11.119. Thermopower of PAiii, PMMA and PET blends with 40% PAni, and polyacetylene doped with MoClS (PAc) and iodine (9, 14 and 27 al.%1). The lines are fils for metallic difFusion thermopower. [Reproduced from ref 101 with kind permission of Elsevier.]...

Naaimann-Polyacetylen , which displayed a particularly high conductivity that was attributed to stretching and orientation processes and to minimal defects in the PAc chains, for an overview cf H. Shirakawa, Y. Zhang, T. Okuda, K. Sakamaki and K. /kkagi, Synth. Met. 65 (2,3), 93-101 (1994). 

ECPs appears in the course of its doping by counterions because of formation of delocalized n-electrons or holes and their transport under the action of electric field through the system of polyconjugated double bonds characteristic of any ECPs. ECPs include polyacetylene (Pac), polyaniline (PAni), poly(p-phenylene) (PPh), polythiophene (PT), polypyrrole (PPy), polyporphyrin (PP), and their derivatives. Eigure 28.3 shows structural formulas for some ECPs used in ECSCs. 

Doping may impose further structural effects that depend on the size and nature of the dopant species. Although there may still not be complete accord on the crystal structure of lithium-doped polyacetylene, it appears that at low doping levels entropic factors are important in inserting a small nonaggregating ion, such as Li", into polyacetylene (PAc), with the dopant occupying sites with minimal strain or disruption of the host lattice. Iodine, on the other hand, in the form of IJ and IJ (and possibly higher polyiodides), produces structures in which anions cluster in columns or sheets to form intercalated layers between polymer chains. ... 

Early versions of ICPs, mostly based on oxidatively doped polyacetylenes (PAcs), faced several intrinsic obstacles that prevented their industrial commercialization. The material degrades readily in air, and no known good methods exist for making easily processable PAc polymers. These obstacles led... 

In the present work we describe the preparation and properties in ethanol conversion of conjugated polymer supported heteropolyanions of Keggin-type structure. Thus 12-molybdophosphoric acid (H3PM012O40) has been supported on polyacetylene (PAc)... 

Conducting polymers (intrinsically conducting polymers, e.g. polyacetylenes (PAC), polypyrroles (PPy), poly thiophenes (e.g poly(3,4-ethylenedioxythiophene) (PEDT), polyanilines (PANI)),... 

Conducting Polymer Polyacetylene (PAc), polyaniline(PAn), polypyrole(PPy) fiber. 10 -10 ... 

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