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2. E. I. du Pont de Nemours, French Patent No. 1,239,491 (1960); Australian Patent No. 58, 424 (1960).
3. A. L. Endrey, Canadian Patent No. 659,328 (1963)
4. U.S. Patent Nos. 3,179,631 and 3,179, 633 (1965).
5. G. W. Bower and L. W. Frost, J. Polym. Sci. A
1, 3135 (1963).