1. U.S.Patent, 3,201,373(1965) (A.C.C.). U.S.Patent, 3,493,548(1970) (Polymer Corp.). Japn. Patent, 48-93687(1973)(Goodrich). etc.
2. U.S.Patents, 3,312,677 (1967)(Thiokol), 3,335,118(1967)(Thiokol), 3,525,721(1970)(Goodrich).
3. Berry, D. D., Rubber World, June, 42(1974). U.S.Patent, 3,487,054(1969)(Goodrich). Japn.Patent 54-28195(1979) (Mitsuboshi).