Other Catalysts for the Polymerization of Acetylene

Several noncatalytic methods for the synthesis of PA are known, including electrochemically forming a PA film on a platinum cathode [52]. This special electrochemical cell uses a platinum cathode, nickel anode, and NiBt2 dissolved in acetonitrile as the electrolyte solution. A 4-40-V potential is then applied across the electrodes to commence the polymerization. The PA film forms on the cathode as a thin black layer and becomes thicker with time. 

Simply increasing the acetylene pressure to beyond a GPa at room temperature inside a diamond anvil will induce self-polymerization [53-55]. Analysis of the resulting materials by Raman spectroscopy indicates that trans-PA is formed predominantly under these conditions, presumably due to steric reasons trans-PA packs better than cis-PA). 

Finally, Soga and co-workers reported the formation of a thin cis-PA film when acetylene gas was exposed to a small amount of ASF5 in a flask at very low temperature (—78°C to —198°C) [56]. The polymer formed in this manner was doped simultaneously (AsFf is a p-dopant (vide infra)) and found to have a conductivity r = 4.8 X 10 S/cm. Polymerization was not observed with other p-dopants such as SO3 or I2 (in place of the AsFs). Researchers proposed that the ASF5 and acetylene first reacted to form a charge transfer complex that initiated the polymerization. 

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