1. Monsanto, UK Patent No. 1357406 (1971).
2. Idemitsu Kosan Co. Ltd., (a) Japanese Patent No. 60/35095 (1985),
3. US Patent No. 4525290 (1985).
4. Nippon Petrochemicals Co. Ltd., Japanese Patent No. 60/86197 (1985).
5. Nippon Steel Chemical Co. Ltd./Mitsubishi Co. Ltd., Japanese Patent No. 61/81492 (1986).