abstract |
A water-isoluble hydrogel, obtained by cross-linking a polyvinyl alcohol by itself, a polyvinyl pyrrolidone by itself, and a polyvinyl alcohol and a polyvinyl pyrrolidone as a pair by exposure to radiation to a cross-linking degree enough for occlusion therein of 50 to 99% by weight of water and they freezing and thawing the product of said cross-linking, production thereof, and an untrasonic transmission medium using the hydrogel. |