Novel cellulose ether hydrogels were prepared by the radiation-induced cross-linking of hydroxypropyl methylcellulose phthalate (HPMCP) in a solution of Na2CO3. The effects of several factors, such as the HPMCP concentration, Na2CO3 concentration, absorbed dose, and dose rate, on the crosslinking of HPMCP were investigated in detail. An increase in the HPMCP concentration resulted in an increasing content of the gel fraction, and this meant that the crosslinking probability increased as well. Na2CO3 was essential for dissolving HPMCP in water, and a 4-5% Na2CO3 aqueous solution was optimal for the crosslinking of HPMCP. The dose rate also affected the radiation crosslinking of HPMCP; hydrogels with higher gel fractions and transparency could be formed at lower dose rates. The ratio of degradation to crosslinking of the gel was calculated according to the Charlesby-Rosiak equation, and it showed good agreement with the experimental results. Some important properties, such as the swelling kinetics, ion and ionic strength dependence, and pH dependence, of the HPMCP hydrogels were also investigated. The HPMCP hydrogels possessed excellent swelling rates and swelling ratios in some solvents, such as water and methanol, with a high hydrogen-bonding parameter. (C) 2003 Wiley Periodicals, Inc.