1. Encyclopedia of Chemical Technology. John Wiley and Sons, Inc., New York, 1985 p. 218.
2. Encyclopedia of Polymer Science and Engineering. John Wiley and Sons, Inc., New York, 1990, pp. 739, 741, 743.
3. & Ger. (East) Patent, DD 283, 046, 1990.
4. & Jpn. Patent, JP 02, 303, 983, 1990.