Radiation crosslinking of carboxymethylcellulose of various degree of substitution at high concentration in aqueous solutions of natural pH

Carboxymethylcellulose (CMC) hydrogel formed by ionizing radiation at highly concentrated aqueous solutions was found to undergo swelling depending on the pH of the swelling media. Swelling increases at neutral and basic pH due to ionization of carboxymethyl groups on side chains. The presence of charges develops repulsive forces between polymer chains of the network causing its expansion. Hydrogel in relaxed state as well as dried gel reveals good mechanical properties. It was considered that intermolecular crosslinking reactions occur by a radical route. Radicals placed on anhydroglucose repeating unit as well as on side chains were distinguished from ESR spectra of CMC. A stable doublet signal with 2.0mT splitting constant belongs to a radical placed on the alpha-carbon atom of the substituent group, R-O-(.)CH-COO(-). It was assumed that this species participates in intermolecular crosslinking. (C) 2003 Elsevier Ltd. All rights reserved.