Crystalline Iodine Complexes of Amorphous Poly(vinyl acetate) as Studied by X-ray Diffraction, Vibrational Spectroscopy, and Computer Simulation

Abstract

One of the typical amorphous polymers, atactic poly(vinyl acetate) (PVAc) has been found to form the two types of crystalline iodine complexes (α and β forms) with iodine ions when the sample is immersed into the iodine aqueous solutions of low and high concentrations (0.001−0.01 and 0.04−3 mol/ L), respectively. By analyzing the experimental data of resonance Raman spectra and X-ray 00L diffractions, the iodine species were identified as I 5− ions in the β form, and the mixture of I 3 − and I 5 − ions was in the α form. The quantitative analysis of the two-dimensional X-ray diffraction data combined with the density functional theory (DFT) calculation gave the two representative models for the iodine complex: in one model (interchain iodine model), the helical PVAc chains of irregular configuration are arrayed side by side, and the iodine columns are sandwiched between these chains. Another model (intrachain iodine complex model) consists of the doubly stranded helices of PVAc chains, inside which the I 5 − (and I 3 − ) ions are confined along the chain axis. Both of these two models reproduced the observed X-ray diffraction data well, suggesting the hybridized model of these two candidates as the more realistic complex model. The details of the packing mode of PVAc chains and iodine columns in the complex are different between the α and β forms. The occupancy of iodine ions is also different between the α and β forms. It is emphasized that the amorphous PVAc chains can form the crystalline complexes with iodine ions although the PVAc chains themselves are totally irregular in configuration. The stabilization mechanism of the iodine complexes of the structurally irregular PVAc chains was discussed on the basis of DFT calculation.

Antimicrobial Biomaterial on Sutures, Bandages and Face Masks with Potential for Infection Control

“…The UV-visible spectrum of AV-PVP-TCA-I 2 reveals absorption peaks of molecular I 2 (207 and 210 nm), iodide ions (202 nm) and triiodide ions (290 and 359 nm) ( Figure 6 , Table 2 ). Iodide ions, iodine molecules and triiodide ions are detected in accordance with previous investigations ( Figure 6 , Table 2 ) [ 15 , 22 , 23 , 25 , 27 , 30 , 33 , 34 , 36 , 41 , 42 , 89 , 90 , 91 , 100 , 101 , 102 , 103 , 104 ]. The bands at 290 and 359 nm depict a higher availability of symmetrical, linear triiodide ions (I-I-I − ) compared to asymmetric triiodide ions and iodine.…”

“…Iodine, a well-known microbicide, is marketed in the form of different iodophors and polymeric complexes [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. Antiseptic iodophors are unaffected by microbial resistance mechanisms and can be utilized to overcome AMR [ 19 ].…”

Structure and Formation Mechanism of Iodine Complexes of Nylon Model Compounds as Revealed by X-ray Single-Crystal Structure Analysis and Density Functional Theory

“…The following two types of low-molecular-weight model compounds of nylon 66 were synthesized, denoted N66NN and N66CC, respectively. The single crystals of pristine N66NN and N66CC were grown from chloroform solution at room temperature. The single crystals of iodine complexes of these compounds were prepared by immersing the original single crystals in HI/I 2 aqueous solutions of 3 M iodine at room temperature (the preparation of single crystals was impossible for the iodine complexes of these model compounds when the KI-I 2 solution was used, as reported in references − ). The original crystal was once dissolved into the solution quite slowly in a few days, from which single crystals of almost black color were obtained after the long time passage, about several weeks.…”

“…One of the most typical dopants may be an iodine ion, as seen in the polyacetylene – iodine complex. , In this case, almost fully extended polyacetylene chains are surrounded by the iodine rod ions, and the electrons are transferred from iodine to the polyacetylene chain via the so-called charge-transfer mechanism. − Another popular iodine complex is seen for starch and amylose, in which the long helical chain encloses many iodine rods along the chain axis. − This case is different from the iodine complex of cellulose, in which the extended cellulose chains are coordinated side by side through interactions with the iodine rod ions in the crystal lattice . From a practical viewpoint, the iodine complex of the polymer is useful in industrial applications. − For example, the highly oriented poly­(vinyl alcohol) (PVA) – iodine complex is utilized widely as an optical polarizer. − The detailed structural analysis of the iodine complexes of PVA and related poly­(vinyl acetate) helped reveal the origin of the optical polarizer at the atomic level, as reported in various papers. − …”

“…63,74,75 The Raman spectra of these iodine complexes are shown in Figure 5a, where the Raman bands observed for PVA−iodine complexes are also compared for reference. [42][43][44][45][46][47][48][49]75 In the latter cases, the crystal forms I, II, and III, produced from the iodine solutions of high concentrations (0.1−3 M), possess the I 3 − ions, as known by the X-ray data analyses. On the other hand, in the crystal form IV produced from the 0.01 M concentration, I 5 − ions are mainly present.…”