1. M. Matsui, T. Yoshikawa, Y. Funaishi, Japanese Patent 52-32799 (1977); Mitsubishi Kasei.
2. Die Polymerisation des Tetrahydrofurans
3. T. Shono, Y. Hachihama, Japanese Patent 35-13940 (1960).
4. H. Mueller, O.H. Huchler, H. Hoffmann, US Patent 4,189,566 (1980); BASF.
5. A. Aoshima, S. Tonomura, R. Mitsui, Japanese Patent 63-30931 (1988); Asahi Kasei.