CONFORMATIONAL CHANGE ON POLYMER-CHAINS OF PARTIALLY FORMALIZED POLY(VINYL ALCOHOL)-IODINE COLOR COMPLEX STUDIED BY USING SYNCHROTRON-RADIATION SMALL-ANGLE X-RAY SOLUTION SCATTERING

The structure of a partially formalized poly(vinyl alcohol) (PFV)-iodi ne color complex was investigated at a series of iodine concentrations by using small-angle X-ray scattering and resonance Raman methods. Sc attering experiments show that the increase of iodine concentration in duces a structural change of the PFV polymer chains from an expanded c oil to a Gaussian coil. On the process of complexation of PFV with iod ine, the number of iodine atoms occluded by a PFV molecule with degree of polymerization (D. P.) 560 was evaluated to be less than 25 (0,044 /D. P.) in the amorphous state or 31 (0,056/D. P.) in the crystal stat e, a value being much smaller than those deduced for amylose and cyclo dextrin. The resonance Raman spectrum of the PFV-iodine complex clearl y indicates the presence of polyiodine chains in the polymers. Therefo re, it can be assumed that the heterogeneous occlusion of iodine in po lymer chains occurs cooperatively, and that the formation of polyiodin e chains changes the local structure of the polymer chains breaking th e long-range interactions between the polymer segments for exhibiting an excluded volume effect.