Polyacetylenes strength

The polymers which have stimulated the greatest interest are the polyacetylenes, poly-p-phenylene, poly(p-phenylene sulphide), polypyrrole and poly-1,6-heptadiyne. The mechanisms by which they function are not fully understood, and the materials available to date are still inferior, in terms of conductivity, to most metal conductors. If, however, the differences in density are taken into account, the polymers become comparable with some of the moderately conductive metals. Unfortunately, most of these polymers also have other disadvantages such as improcessability, poor mechanical strength, instability of the doped materials, sensitivity to oxygen, poor storage stability leading to a loss in conductivity, and poor stability in the presence of electrolytes. Whilst many industrial companies have been active in their development (including Allied, BSASF, IBM and Rohm and Haas,) they have to date remained as developmental products. For a further discussion see Chapter 31. 

Whilst the conductivity of these polymers is generally somewhat inferior to that of metals (for example, the electrical conductivity of polyacetylenes has reached more than 400 000 S/cm compared to values for copper of about 600 000 S/cm), when comparisons are made on the basis of equal mass the situation may be reversed. Unfortunately, most of the polymers also display other disadvantages such as improcessability, poor mechanical strength, poor stability under exposure to common environmental conditions, particularly at elevated temperatures, poor storage stability leading to a loss in conductivity and poor stability in the presence of electrolytes. In spite of the involvement of a number of important companies (e.g. Allied, BASF, IBM and Rohm and Haas) commercial development has been slow however, some uses have begun to emerge. It is therefore instructive to review briefly the potential for these materials. 

The stress-strain curves of the vulcanizates with 40 phr filler loading are shown in Fig. 28. SBR reinforced with plasma-coated carbon black shows a slight improvement in tensile strength relative to SBR with uncoated carbon black. Polyacetylene-coated carbon black can better interact chemically and physically with the elastomer and thus contributes extra to the reinforcement of the elastomer. 

Pleated sheet conformation, 30,31 PLEDs (polymeric light-emitting diodes), 218 Plexiglas, 62 Plunkett, Roy, 65-66 PMMA. See Poly(methyl methacrylate) Polartec (Polar Fleece), 194 Poly(6-aminohexanoic acid), 25 Poly(a methyl styrene), 20 Polyacetylene, 72, 73 Polyacrylamide, 20 Polyamides, 22, 28, 61, 146 biodegradable, 185 Polyaramids, 77, 86 Polybutadiene, 70,109,148,155 Poly butyl acrylate), 20 Poly(butylene isophthalate), 25 Polycaprolactam, 21 Polycarbonate (PC), 17, 48, 86, 140 biodegradable, 185 density of, 247 impact strength of, 143 permeability of, 163 Polychloroprene, 65 Polycondensation, 85, 90-91 interfacial, 91-92... 

In the case of a polymer with a saturated chemical structure, such as polyethylene, the strength of a-bonding is such that the band gap will be comparable to that in diamond. However, for a polymer with a conjugated structure, such as polyacetylene, the chemical binding of the re-electrons is much weaker and a gap of a few eV, comparable to those in inorganic semiconductors, is anticipated. 

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

As noted above, the free carrier contribution which extrapolates to the measured a(0) must be in the far-IR below 450 cm"1.15 Nevertheless, most of the 7C-electron oscillator strength remains in the broad absorption band above 0.2 eV. An alternative which appears to be in agreement with the essential experimental facts is that polyacetylene is an example of a polaronic metal. The polaron lattice with a half-filled polaron band is certainly consistent with the observed susceptibility, hi the case of a polaron lattice, the IRAV modes are expected, and would be r -shifted from the Raman modes provided that the pinning is weak. Although the intensity of the IRAV modes was initially csdculated to be much too weak, this calculation ignored the effect of the counter-ions the counter-ion Coulomb potentials may lead to sufficient nonuniformity in the charge density, to yield the observed IRAV mode intensities.For the polaron lattice, a((o) would have two contributions with a "gap" in between ... 

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