1. Boor, J., Jr.: The Nature of the Active Site in the Ziegler-Type Catalyst, J. Polymer Sci., Part D 2, 115 (1967).
2. This article contains a very large number of references on earlier works. For more recent literature, see e.g.: Boor, J., Jr.: Ind. Eng. Chem. Prod. Res. Develop. 9, 437 (1970).
3. Tsuruta, T.: J. Polymer Sci., Part D 6, 179 (1972).
4. Natta, G., Corradini, P.: Atti Accad. Naz. Lincei, Memorie (8), 4, 73 (1955).
5. Natta, G., Pino, P., Corradini, P., Danusso, F., Mantica, E., Mazzanti, G., Moraglio, G.: J. Am. Chem. Soc. 77, 1708 (1955).