STEREOSPECIFIC CHLORINATION OF POLYACETYLENE BY CHEMICAL DOPING

We present a novel utilization of chemical doping in stereospecific chlorination to pi-conjugated polyene. It has been verified that not only prolonged FeCl3 doping but also iodine doping followed by chlorine addition to one-dimensional conjugated polyene (polyacetylene, (CH)x) produce a stereoregular chlorinated polyacetylene, (CHCl)x, i.e. di-syndiotactic poly(1,2-dichloroethylene). In the latter case, tacticity of the polymer, defined as the ratio of stereoregular to atactic segments in the (CHCl)x, strictly depends upon the dopant concentration of iodine before the chlorine addition. Thus chemical doping is a promising method to control the tacticity of (CHCl)x without polymerization. We demonstrate that the positively charged polyene segment generated by the chemical doping plays an essential role in governing stereospecific chlorination.