On the intermolecular crosslinking of PVA chains in an aqueous solution by γ-ray irradiation

Abstract

We studied how the polymer chains of poly(vinyl alcohol)(PVA) are crosslinked in its O2-free aqueous solution by γ-rays. The static–dynamic laser light scattering method was employed for determining the molecular weight (Mw), hydrodynamic radius (Rh) and radius of gyration (Rg) for the original PVA (Mw=1.0×105) and its radiation products. The γ-ray irradiation from Co60 to the PVA solutions with different concentrations was performed at different dose levels. It was found that both molar mass and size (i.e., Rg and Rh) of the radiation products increased with a dose increase. The magnitude of these increases was enhanced by decreasing the polymer concentration (Cp). In particular, at Cp< the critical polymer concentration leading to microgel formation, very rapid increases in mass and size were observed even at a low dose level. In order to obtain more detailed information about the irradiation-induced crosslinking of PVA, we studied the dose dependence of the molar concentration of intermolecular crosslinks in the system as a function of Cp using the dose curves of Mw. It became apparent that, regardless of Cp, the intermolecular crosslinking reactions were dominant in the initial stage of irradiation. The radiation yield of intermolecular crosslinking was found to increase linearly when increasing Cp, and at Cp> the overlap concentration it asymptotically approached a limiting value estimated from the dimerization of pentane-2,4-diol as a model compound of PVA.