1. Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan; Structural Materials Science Laboratory, SPring-8 Center, RIKEN Harima Institute Research, Hyogo 679-5148, Japan; and Advanced Science Reserch Center (ASRC), Japan Atomic Energy Agency (JAEA), Tokai-mura, Ibaraki-Pref. 319-1195, Japan