1. 1Faculty of Engineering, Nagaoka University of Technology Nagaoka, Niigata 940-2188, Japan; email:kawahara@chem.nagaokaut.ac.jp
2. 2Department of Chemistry, Faculty of Science, Mahidol University Rama VI Road, Bangkok 10400, Thailand
3. 3Technology and Engineering Division, Malaysian Rubber Board 260, Jalan Ampang, 50450 Kuala Lumpur, Malaysia