Cis-polyacetylene

Growth mechanism of a (9n,0) tubule, over 24n coordination sites of the catalyst. The growth of a general (9 ,0) tubule on the catalyst surface is illustrated by that of the (9,0) tubule in Fig. 16 which shows the unsaturated end of a (9,0) tubule in a planar representation. At that end, the carbons bearing a vacant bond are coordinatively bonded to the catalyst (grey circles) or to a growing cis-polyacetylene chain (oblique bold lines in Fig. 16). Tlie vacant bonds of the six c/s-polyacetylene chains involved are taken to be coordinatively bonded to the catalyst [Fig. 16(b)]. These polyacetylene chains are continuously extruded from the catalyst particle where they are formed by polymerization of C2 units assisted by the catalyst coordination sites. Note that in order to reduce the number of representations of important steps, Fig. 16(b) includes nine new Cj units with respect to Fig. 16(a). 

The 12 catalyst coordination sites — drawn further away from the surface of the particle (closer to the tubule) — are acting in pairs, each pair being always coordinatively bonded to one carbon of an inserted (F) or of a to-be-inserted (2 ) Cj unit and to two other carbons which are members of two neighbouring cis-polyacetylene chains (3°). It should be emphasized that, as against the (5n,5n) tubule growth, the C2 units extruded from the catalyst particle are positioned in this case parallel to the tubule axis before their insertion. 

Polythiophene is a highly crystalline polymer with the chain analog to cis-polyacetylene. The sulfur atoms stabilize the structure and interacts poorly with... 

Fig. 14a-c. Crystal structures of a /ranr-polyacetylene, b cis-polyacetylene and c polyphenylene. Reproduced with permission a from Ref.6) p. 103, b and c from Ref. 2861... 

Fig. 5 The observed and calculated components of the I3C shielding tensors of cis- and /ra s-polyacetylenes. The directions of the principal axes are indicated at the bottom( the angles between the C-H bond and the direction of oH for trans- and cis-polyacetylenes are 16°and 17°, respectively).

The other isomer is called cis-polyacetylene. This has a slightly different structure with non-degenerate ground state energy. 

Figure 2 cis-Polyacetylene structures regular (Model III) trans-cisoid (Model IV) and cis-transoid (Model V). The unit cells are surrounded by broken lines... 

Acetylene selectivity polymerizes in the presence of Ziegler catalysts whose components have low Lewis acidity [e.g., Ti(0-n-Bu)4—Et3Al(l 4)J. Cis-polyacetylene forms at low temperature, and trans-polyacetylene at high temperature (Eq. (1)). When doped, a polyacetylene film shows metallic conductivity, and hence the application of polyacetylene to polymer batteries and solar cells is now under intensive study 1-3). 

The irreversible transformation of cis-polyacetylene into the trans-modification has been studied by Riekel. A sequence of selected diffraction patterns which were obtained upon heating the sample from room temperature to about 350 °C with a heating rate of 11 °C min" is shown in Fig. 57. At about 150 °C the rate of cis/trans... 

Fig. 57 a and b. Change of the diffraction pattern of cis-polyacetylene upon heating from room temperature with 11 °C min" The cis/trans isomerization is indicated by the disappearance of the 201 reflection at about 150 °C. Above about 290 °C a broad peak indicates decomposition... 

The reaction of cis-polyacetylene with Iodine vapour has been studied by Riekel. 

Fig. 58. Change of the diffraction pattern of cis-polyacetylene upon chemical reaction with 12-vapour at room temperature An analysis...

Polythiophene (PT) 20 can be regarded as a hybrid structure of cis-polyacetylene and sulfur, where the incorporation of the heteroatom leads to a much higher environmental stability of PT compared with that of PA [131], The outstanding physical and bulk properties make PT a desirable material for device applications like sensors, energy storage, solar cells, LEDs, NLO devices, and more [132], Due to the large number of possible technical applications, much effort has been made to tailor the properties of PT by synthesis. 

CIS-POLYACETYLENE. 0 FUSED QUARTZ. POLYVINYL CHLORIDE - - 10 WHITE PHOSPHORUS -... 

Fig. 16.1. " C CP/MAS NMR spectra of partially isomerized polyacetylenes (a) pure cis-polyacetylene (b) partially isomerized polyacetylenes of initially high cis content and (c) pure tranr-polyacetylene.

It is accepted that the actual frans-polyacetylene crystal has two chains in the cell, the centre chain rotated with respect to its four nearest neighbours, similar to cis-polyacetylene. Such a cell is often found for planar zigzag chains, e.g. polyethylene. In three dimensions, inclinations similar to the ones discussed above are induced by the packing of short and long... 

F. lOs, b. pS Relaxation and pS Repolarization of polyacetylene, (a) Mu addition to cis-polyacetylene leads to Mu-substituted radicals formation. Consequently the asymmetry is increased (Repolarization) at higher magnetic field intensity, but there is no relaxation of p spin, (b) Mu adds to troKs-acetylene, but there are no stable Mu-substituted radicals because the unpaired electron goes into a soliton movement, p spin is repolarized at high magnetic fields, but there is an apparent relaxation caused by the random walk of the unpaired electron... 

Solutions of complex compound cyclopentadienyl-dititana in hexane and sodium cyclopentadienyl complex have high catalytic activity. Films with a metallic luster can be obtained by slowly removing the solvent from the formed gel polyacetylene in vacuum. It is assumed that the active complex has a tetrahedral structure. Polymerization mechanism is similar to the mechanism of olefin polymerization on catalyst Ziegler-Natta. Obtained at -80°C cis-polyacetylene films after doping had a conductivity of 240 (Ohm-cm" ). 

Polyacetylene films were able to s mthesize on an internal surface of a reactor in an interval of temperatures from -78 up to -198°C at addition of acetylene to arsenic pentafluoride. Strips of absorption cis-polyacetylene are identified in the field of 740 cm and doped complexes in the field of 900 and 1,370 cm". ... 

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