Polyacetylene, dispersion

For silica in SBR, a polyacetylene coating gives the lowest filler-filler interaction, a good filler-polymer interaction, and the best dispersion compared to untreated and the other plasma-treated samples. However, for the stress-strain properties, the polythiophene-treated sample gives the best results. This shows the importance of sulfur moieties on the surface of the filler, which form a secondary network in the cured materials. In the blend of S-SBR and EPDM rubbers, the situation is less conclusive. The Payne effect, the bound rubber, and... 

Application of a plasma coating onto carbon black is very difficult compared to silica. It was only practically feasible for fullerene soot (left over from the fullerene production), which contains a large amount of reactive groups on its surface. Polyacetylene-plasma-treated fullerene soot provides an improved dispersion in SBR and in a SBR/EPDM blend compared to untreated fullerene black. However, the effect on the stress-strain properties is rather limited and the coating has only a slight effect on the final properties. 

The soliton conductivity model for rrans-(CH) was put forward by Kivelson [115]. It was shown that at low temperature phonon assisted electron hopping between soliton-bound states may be the dominant conduction process in a lightly doped one - dimensional Peierls system such as polyacetylene. The presence of disorder, as represented by a spatially random distribution of charged dopant molecules causes the hopping conduction pathway to be essentially three dimensional. At the photoexitation stage, mainly neutral solitons have to be formed. These solitons maintain the soliton bands. The transport processes have to be hopping ones with a highly expressed dispersive... 

A soliton is a giant solitary wave produced in canals by a cancellation of nonlinear and dispersive effects. The connection between aqueous solitons and tsunamis ("harbor waves") is not definitively established. In "doped" conducting polyacetylene, a neutral soliton is a collective excitation of a polyacetylene oligomer that has amplitude for several adjacent sites [57],... 

Carbene or cuprene are technical names for polyacetylene. It is obtained as a cork-like substance, which is in a very fine state of dispersion, by polymerizing acetylene on copper catalysts. 

Fig. 19. Resonant scattering, absorption and fluorescence of iodine in a 100 pm foil of polyacetylene, CHJ j, near the Lj-absorption edge (X = 2.72 A) at h = 0.1 The very high dispersion of fluorescence and absorption at the short wavelength side of the absorption edge limits the measurement of resonance scattering to the pre-edge region of the spectrum. ( + ) f (E) S,...

Figure 8 presents the temperature dependence of the dynamic viscoelasticity of the Si-containing polyacetylenes (23, 24). Poly(2c) shows a dispersion at low temperature because of the presence of the long n-pentyl group. From the sharp increase in tan 8, the glass transition temperature (Tg) of this polymer is about 150 °C. In contrast, poly(3) and poly(4a) hardly show dispersions at low temperature, and their TgS are about 200 or higher. The high Tg values of these polyacetylenes compared with those of most vinyl polymers can be attributed to their stiff main chain. 

Suspensions of polyacetylene were prepared as burrs or fibers (46) by using a vanadium catalyst. When the solvent was removed, films of polyacetylene were formed with densities greater than that prepared by the Shirakawa method. These suspensions were mixed with various fillers to yield composite materials. Coatings were prepared by similar techniques. Blends of polypyrrole, polyacetylene, and phthalocyanines with thermoplastics were prepared (47) by using the compounding techniques typically used to disperse colorants and stabilizers in conventional thermoplastics. Materials with useful antistatic properties were obtained with conductivities from 10" to 10" S/cm. The blends were transparent and had colors characteristic of the conducting polymer. For example, plaques containing frans-polyacetylene had the characteristic violet color exhibited by thin films of solid trans-polyacetylene. 

Polyacetylene latexes (48) have been prepared by polymerizing acetylene in the presence of poly[(fert-butylstyrene)-fo-(ethylene oxide)]. The use of a tetrahydrofuran/cyclohexane (THF/cyclohexane) solvent combination led to the formation of a stable dispersion of nearly uniform spherical polyacetylene particles 40-200 nm in diameter. The block copolymer was separated from the polyacetylene by several wash cycles with a good solvent for the block copolymer (cyclohexane), and after removing the solvent, a polyacetylene powder was obtained. On the basis of nitrogen adsorption... 

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. 

Early work on polyacetylene was only able to cover part of the spectral range and apparently suffers fi"om a calibration error [28]. Fig. 10.17a shows the INS spectrum of polyacetylene [29] recorded on TFXA. The spectrum in the region below 700 cm is remarkable in that it consists of a series of terraces, each terminating in a bandhead. This is reminiscent of the Vs mode of polyethylene and suggests that the modes are strongly dispersed. This is confirmed by the dispersion curves [30], and the resulting INS spectrum calculated from them. Fig. 10.17b and c. 

A structural model, based on a complex process of stretch induced ordering in the polyacetylene domains, was proposed to account for these observations. Support for this model was obtained using electron microscopic techniques. Low polyacetylene content blends (<20% PA) were found to consist of discrete polyacetylene domains dispersed in a continuous polybutadiene matrix. In the high polyacetylene content blends (>70% PA), both phases were simultaneously continuous, forming an interpenetrating network structure. Blends with intermediate compositions consist of both continuous and isolated domains of polyacetylene distributed throughout the polybutadiene matrix. 

It is possible, however, to blend these intrinsically brittle polymeric conductors with polymers that enhance their mechanical properties. In the case of polyacetylene, this has been accomplished by polymerizing acetylene gas in the presence of a suitable host polymer, (5-7) Since polyacetylene is actually grown in the matrix of the host polymer, and not simply physically dispersed, the resultant morphology of the polyblend (and, hence, the electrical and mechanical properties of the system) can be manipulated by adjusting the reaction conditions. In addition, by proper selection of the blending component, it is possible to further modify the properties of the polyblend by physical means. 

The highest value of 7 found in a study of quadrupolar examples (THG at 1,907 nm) was 229 x 10 esu for 225, which was the longest system studied. The third-order susceptibility, (DFWM, 532 nm), for the polymer, 226, was found to be over 1,000 times that of all-trans polyacetylene, although this value is presumably dispersion enhanced and very far from the static value. " ... 

Fig. 2.6. The energy level diagram for (a) an unphysical infinite one dimensional metallic version of polyacetylene and (b) the more realistic dimerized polyacetylene molecule. The monomeric uniform molecule does not exhibit a bandgap because of its infinite size. A HOMO-LUMO gap exists despite the infinite extent of the molecule because of the Pierels instability which dimerizes the molecule and separates the bands at the Brilloin zone edge. These dispersion relationships are calculated using the derivation presented in [9] and [10].

The electric modulus approach (AT = 1/e ) used in the case of polyacetylene [3] has shown that this contribution is more important. With the assumption of a conductivity distribution, this description allow the explanation of the dispersion of t with frequency without any molecular polarisation phenomenon. 

Polymeric catalysts were also synthesized by fixing metal compounds (Wilkinson catalyst, tertnuclear carbonyl cluster M0CI5, Ni(acac)) onto the surfaces of polyethylene [30-32], polyacetylene [33], teflon [34], and polydibenzo-18-crown-6 [35]. In each case, the activity of dispersed catalysts was higher than that of the homogeneous catalysts. 

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