TRANSFORMATIONS BETWEEN POLYIODIDE STRUCTURES IN A NYLON-6 MATRIX

Nylon 6 (N6) can incorporate up to 1.4 times its weight of iodine, and this is the highest reported for any polymer-iodine complex. Structur es of these complexes are investigated by X-ray diffraction. Iodine ex ists in the N6 matrix as iodide ions between hydrogen bonded sheets. T he heavily iodinated N6 (1.25 mol of iodine/chemical repeat of N6) sho ws an equatorial period of 23 angstrom which we attribute to the prese nce Of I5- arrays perpendicular to the chain axis. The complex rapidly loses iodine during initial aging and becomes fairly stable once a co ncentration level of ca. 0.75 mol of iodine is reached. During this in itial aging, the I5- arrays transform into I3- species but maintain th eir orientation and thus result in a structure with an equatorial 15.6 angstrom repeat. As the concentration of the iodide ions is further r educed by continued aging (0.25 moles), the I5- columns are establishe d parallel to the chain axis, resulting in a structure with an equator ial repeat of 8 angstrom. Thermal data show that the transition from I 3-(perpendicular-to) to I5-(parallel-to) is the result of ''melting'' and ''recrystallization'' of the iodide ion arrays. The gamma form of N6 is obtained as the iodide ions are removed from the 8-angstrom stru cture. A lattice match between the I5-(parallel-to) ions and the chain -axis structure of N6 in the final stage of the complex is thought to be responsible for the formation of they crystalline form of N6 from t he iodinated complex.