STRUCTURAL VARIATIONS OF ORIENTED POLYACETYLENE UPON INTERCALATION WITH SELECTED ELECTRON DONATING AND ACCEPTING SPECIES

Unaligned and highly oriented polyacetylene (HOPA) have been doped with a heavy alkali metal M in the vapour phase. The evolution of the crystallographic structure of these polyacetylenes during the progress of the intercalation has been studied by X-ray diffraction. Different ordered and partially ordered phases have been characterized depending on the dopant concentration. Our results support the channel intercalation model and allow the description of the mechanisms of (CH)x doping. First, at the beginning of doping the alkaline ions enter into the channels; their separation distance in the chain direction is equal to 4 (CH) units; only a short-range 2-D order perpendicular to the chains corresponds to the selective filling of one channel among the two possible available ones, which leads to the tetragonal lattice of the ideal (M(C4H4)4)x compound in agreement with the corresponding slope observed in potential versus composition curves. Secondly, upon higher doping there is the apperance of a 3-D order where the columns of alkaline ions separated by 4 (CH) units fill up equally the available channels in a centred tetragonal cell; the formula of this commensurate compound is represented by (M(C4H4)2)x. Finally, more extended doping results in loss of the commensurability of the alkaline ion and polymer lattices, in the chain direction; at this time the distance between the alkaline ions becomes near to 3 (CH) units leading to the limiting formula (M(C3H3)2)x. These two latest formulae agree with the limiting richest compositions of the slope region observed in the potential versus composition curves. Preliminary structural data are also reported on the incommensurate GaCl4--(CH)x products synthesized electrochemically in LiGaCl4CH3NO2 electrolyte. © 1990.