Polyacetylene fiber

The work of Kim et al. [110] focused on pofyacetylene fiber networks ranging in diameter from 60 to 80 nm. The dark red gel of low density foamlike polyacetylene doped with iodine showed a remarkably low temperature dependence of resistivity as compared to bulk polyacetylene film. Polyacetylene fiber networks were found to be more sensitive to air than the bulk polymer, because the resistance of the iodine-doped fiber network increased more rapidly than that of the bulk polyacetylene film on mqposure to air. 

Fig. 5.9 Schematic representation of a polyacetylene fiber with O2 impurities bonded to the surface. Soliton traps are created on (CH), chains, with trapping energy that is a function of r - ro, the chain-to-surface distance. (From Ref. 56.)...

Poly(4-phenoxybenzoyl-1,4-phenylene) (PPBP), sulfonated, 23 718 Polyacetal, antioxidant applications, 3 121 Polyacetaldehyde, 1 103 Polyacetal fiber, 13 392 Polyacetylene, 7 514-515 26 953 conduction in, 7 527 22 208 molecular structure of, 22 211 optical band gap, 7 529t Peierls distortion in, 22 203, 208 room temperature conductivity, 7 532 synthesis of, 22 213... 

Most carbon fibers use PAN as their precursor however, other polymer precursors, such as rayon [8], pitch (a by-product of petroleum or coal-coking industries), phenolic resins, and polyacetylenes [6,7], are available. Each company usually uses different precursor compositions for its products and thus it is difficult to know the exact composition used in most commercially available carbon fiber products. 

POLYACETYLENE. A linear polymer of acetylene having alternate single and double bonds, developed in 1978. It is electrically conductive, but this property can be varied in either direction by appropriate doping either with electron acceptors (arsenic pentaflnoride or a halogen) or with electron donors (lithium, sodium). Thus, it can be made to have a wide range of conductivity from insulators to n- or >-type semiconductors to strongly conductive forms, Polyacetylene can be made in both cis and trans modifications in the form of fibers and thin films, the conductivity... 

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. 

A triumph of the Durham route was the preparation of oriented crystalline polyacetylene (107-109) by stretch orientation of the polymer during the transformation reaction. This material has highly anisotropic optical properties, but the anisotropy of the conductivity of the doped polymer was low. Oriented fibers as well as films were prepared. 

Sliva, D.E. Selley, W.G. Continuous Method for Making Spinnable Polyacetylene Solutions Con-vertable to High Strength Carbon Fibers. US Patent 3928516, 1975. 

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. 

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). 

The advantages of the Durham route are (1) contaminating catalyst residues can be removed because the precursor polymers are soluble and can be purified by dissolution and reprecipitation and (2) the precursors can be cast as films or drawn and oriented prior to conversion to the all-trans form of polyacetylene. This allows a degree of control over the morphology of the final product which in the pristine state appears to be fibrous and disordered. Because conductivity increases by alignment of the polymer chains, stretching the film or fiber assists this process and this can be performed using the prepolymer. 

Though the rate of diffusion for a doping agent in polyacetylene itself is very low (D= cm /s for Li in polyacetylene), it is compensated for by the fiber structure, which reduces the diffusion length when the material is impregnated with a liquid electrolyte. 

Kwak, G., Fukao, S., Fujiki, M., Sakaguchi, T., Masuda, T. Nanoporous, honeycomb-structured network fibers spun from semiflexible, ultrahigh molecular weight, disubstituted aromatic polyacetylenes superhierarchical structure and unique optical anisotropy. Chem. Mater. 18, 5537-5542 (2006)... 

Percec and coworkers have shown that the oriented fibers of dendronized polyacetylenes can undergo thermally induced mechanical motion [38]. In this system (Figure 37.12), the dendrons around the polymer backbone become self-organized and thus facilitate a reversible ciscoid-to-transoid conformational isomerism of the polymer backbone. This isomerism is then converted into unidirectional macroscopic motion along the fiber axis. Remarkably, this mechanical motion could be used to displace objects with a mass of up to 250-fold that of the polymer fiber. 

Helical polyacetylene (PA), 3-3-3-12, 16-3, 16-6, 16-11 Helical single PA fibers, 16-7 Helical solid, 9-23 Helix Formation, 3-12... 

With regards to the mechanical properties of substituted polyacetylenes, aromatic polymers like poly(diphenylacetylene) derivatives are generally hard and brittle, whereas aliphatic polymers with long alkyl chains like poly(2-octyne) are soft and ductile.Considerations of mechanical properties are especially important when polymer membranes or fibers are required for the specific application. 

For completeness, after discussing the histories of carbon fibers derived from cellulose, PAN, and pitch, the category of "other precursors" should be covered. The tremendous activity in carbon fiber research and development is reflected in the large number of precursors which have been converted into carbon fibers. Besides the "big three", the list [34] includes phenolic polymers, phenol formaldehyde resin, furan resins [35], polyacenaphthalene, polyacrylether, polyamide, polyphenylene, polyacetylene, polyimide, polybenzimidazole, polybenzimidazonium salt, polytriazoles, modified... 

---