Plastics polyacetylene

Acetylene (ethyne), C2H2, can be polymerized, (a) Draw the Lewis structure for acetylene and draw a Lewis structure for the polymer that results when acetylene is polymerized. The polymer has formula (CH), where n is large, (b) Consider the polymers polyacetylene and polyethylene. The latter has the formula (CH2)W and is an insulating material (plastic wrap is made of polyethylene), whereas polyacetylene is a darkly colored material that can conduct electricity when properly treated. On the basis of your answer to part (a), suggest an explanation for the difference in the two polymers. 

A variety of copolymers of acetylene and other alkynes have been prepared. Copolymers of acetylene and methylacetylene (86), a soluble polyene, were more tractable than polyacetylene itself, but as the fraction of methylacetylene in the copolymer increased, both the tractability and the final conductivity of the iodine-doped polymer decreased. At an acetylene mole fraction of 0.5, the copolymer was insoluble, and the final conductivity had fallen from greater than 100 to 1 S/cm. Some plasticization remained, however, and the polymer could be stretched to elongation ratios as high as 7. Copolymers of acetylene and phenylacetylene containing 26% acetylene were soluble in methylene chloride (24). Like methylacetylene copolymers. 

A battery cell where both the electrodes consist of dopable polymer is shown in Figure 5.23. The electrolyte in this case consists of Li+ClO 4 dissolved in an inert organic solvent, usually tetrahydro-furan or propylene carbonate. When two sheets of polyacetylene or PPP are separated by an insulating film of polycarbonate saturated in an electrolyte (lithium perchlorate), and completely encapsulated in a plastic casing, a plastic battery can be made. The two sheets of polyacetylene or PPP act as both anode and cathode for the battery. A schematic is shown in Figure 5.24. Although doped polyacetylene and polyaniline electrodes have been developed, polypyrrole-salt films are the most promising for practical appKcation. 

An all-plastic battery may have many advantages [26]. For example, a car battery made of polyacetylene could weigh only one-tenth of that of a conventional lead-acid battery. Moreover, batteries with plastic electrodes could be fabricated into odd shapes, such as a flat disc that could be slotted into a car door. Prototype batteries have been made using polyacetylene and poly-p-phenylene electrodes, but a number of technical problems, such as long-term mechanical integrity need to be solved. 

The feasibihty of all-plastic batteries has been demonstrated by construction of such a battCTy from two layers of polyacetylene salt, sandwiching a film of... 

Organic compounds are generally good insulators, and metals conduct electricity. However researchers have been successful in making organic compounds that are conductors. Acetylene can be polymerized in the presence of a catalyst to polyacetylene, a typical plastic that does not conduct electricity. 

The result was a silver film that looked more like a metal than anything else. Furthermore, the polyacetylene film conducted electricity, which was a first for plastic materials. 

Nagatomo, T., G. Ichikawa, and O. Omoto. 1987. All-plastic batteries with polyacetylene electrodes. 7 Electrochem Soc 134 (2) 305. 

---