CRYSTALLINE-STRUCTURE OF POLYACRYLONITRILE IODINE COMPLEX

The existence of structural order is found in the polyacrylonitrile (P AN)-iodine complex obtained by immersing PAN film in an aqueous soluti on of I2/KI. We provide an interpretation for the key features of this structural order and for the structural change of PAN by iodine sorbi ng. The observed diffractions suggest that iodine penetrates into the crystalline phase of PAN at relatively low iodine concentrations and a re intercalated between PAN molecular cylinders in the form of polyiod ine columns that are composed mainly of I5(-) (most likely the I2/I3(- ) complex). Pseudohexagonal crystals of PAN are expanded uniaxially by replacement of PAN molecular cylinders by the polyiodine columns. The intercalated polyiodine column layers are arrayed parallel with PAN c hain layers in the crystalline phase. The results led to a proposal of an intercalation model for the crystalline structure of the PAN-iodin e complex. The crystalline structures are expected to exist with two d ifferent types of the polyiodine layers. The crystalline transition be tween these structures occurs by thermal mobility of PAN chains. (C) 1 994 John Wiley & Sons, Inc.