1. T. I. Bair, P. W. Morgan, U.S. Pat. 3,673,143 (1972); 3,817,941 (1974).
2. K. Shimada, H. M. Mera, N. Sasaki and A. Aoki, U.S. Pat. 4,355,151 (1982).
3. S. Ozawa, Y. Nakagawa, K. Matsuda, T. Nishihara and H. Yuroki, U.S. Pat. 4,075,172 (1980).
4. K. Matsuda, Polym. Prep. (Am. Chem. Soc., Div. Polym. Chem.), 20, 122 (1979).
5. J. Blackwell, R. A. Cageao and A. Biswas, Macromolecules, 20, 667 (1987).