Network structure of swollen iodine-doped poly(vinyl alcohol) amorphous domain as characterized by low field NMR.

The network structure in the amorphous domain of swollen iodine-doped poly(vinyl alcohol) (PVA) was systematically investigated by low-field (LF) NMR techniques to reveal the PVA-iodine complex formation mechanism. Three PVA-iodine complexes were obtained under different iodine concentrations () of KI/I solution: (i) < 0.1 M: PVA-I/I complex only exists in the non-crystalline region, (ii) 0.1 M < < 1 M: formation of PVA-I complex I, and (iii) > 1 M: formation of PVA-I complex II. It was found that there is no intermediate-magnitude chain motion of PVA under dyeing conditions to induce the substance exchange, as evidenced by the unchanged second moment (∼1.2 × 10 m s) at elevated temperature (<380 K). The introduction of iodine ions can affect the chain mobility of the interphase and mobile regions. With increasing , the chain dynamics become more restricted, as detected by the faster decay of the relaxometry results, which further accelerates the complexation process. The residual dipolar coupling strength, , obtained by the more quantitative double-quantum (DQ) NMR, increases abruptly at > 1 M. This suggests more constraints form in the amorphous network for the PVA-I complex II system. The constant defects fraction further reveals that the complexation prefers to happen along the tie chains. These results supply a possible formation pathway for the PVA-iodine complexes.