1. Nippon Shokubai Research Alliance Laboratories Osaka University 2‐1 Yamadaoka Suita Osaka 565‐0871 Japan
2. Superabsorbents Research Department Nippon Shokubai Co. Ltd. 992‐1 Aza Nishioki Okihama, Aboshiku Himeji Hyogo 671‐1282 Japan
3. Department of Applied Chemistry Graduate School of Engineering Osaka University Suita Osaka 565‐0871 Japan