Effects of repeated water exchange and the molecular-weight distribution of PVA cast gels on the elution of polymers

The elution behaviors of polymers from hydrogels are studied using repeated water exchange on poly(vinyl alcohol) (PVA) gels. Physically cross-linked PVA gel was prepared using a cast-drying method from several powders with a high degree of hydrolysis (98.5 mol%) and varying degrees of polymerization (500, 1000, 1700, and 2400). The gels were immersed in water, which was then repeatedly exchanged with and without an immediate drying process. The elution of polymers from a PVA cast gel was estimated by quantitatively measuring the total carbon in the solvent water using a total organic carbon analyzer; a measurement was taken each time the solvent water was exchanged, and the amount of polymers eluted approached zero after sufficient water exchange. The total amount of polymers eluted is dependent on the degree of polymerization of the PVA powders. Additionally, the molecular-weight distributions of the PVA powders used for gelation and the polymers eluted in the solvent water were evaluated using a high performance liquid chromatography. The average molecular-weight of the eluted polymers was less than that of the PVA powders. The elution behaviors during repeated water exchange are discussed on the basis of the amount eluted and the molecular-weight distribution of the eluted polymers; these factors are dependent on the nature of the PVA powders.