“I2-Doping” of 1,4-polydienes

The discovery, in 1988, that “iodine-doped” rubber can conduct electricity attracted a great deal of interest [1,2]. However, it also generated some fundamental questions [2]: First, what is the mechanism from which the conductivity of “I2-doped” rubbers arises? Second, why does cis-1,4-polybutadiene not become electrically conductive by “I2-doping”, but its trans-conterpart does? Third, what is the effect of “I2-doping” and conductivity in the rubber component on rubber-containing conducting composites and/or copolymers? We have previously demonstrated that “I2-doping” of cis-1,4-polyisoprene produces conjugated sequences of unsaturated double bonds in the polymer backbone, which confer conductivity. Recently, we have found that “I2-doping” of cis-1,4-polybutadiene, unlike the trans-isomer, does not lead to the formation of conjugated sequences at room temperature — a finding which leads to the formation of conducting patterns through patterned photoisomerization of cis-1,4-polybutadiene films followed by “I2-doping”. We have also observed, for the first time, the occurrence of “I2-doping” of the polyisoprene component in polyisoprene-polyacetylene copolymers.