1. and U.S. Patent 2,727,884 (to Dow Chemical Co.), Dec. 20, 1955.
2. and U.S. Patent 3,658,946 (to BASF), Apr. 25, 1972.
3. and U.S. Patent 3,903,202 (to Monsanto Company), Sept. 2, 1975.
4. and U.S. Patent 3,945,976 (to Standard Oil Company), Mar. 23, 1976.
5. and U.S. Patent 4,011,284 (to Shell Oil Company), Mar. 8, 1977.