1. G. Natta, in:Catalysis, Vol. 3, ed. P.H. Emmett (Reinhold, New York, 1955) 349;
2. P.K. Frolich, M.R. Fenske and D. Quiggle, Ind. Eng. Chem. 20 (1928) 694;
3. P.K. Frolich, M.R. Fenske, P.S. Taylor and C.A. Southwich, Jr., Ind. Eng. Chem. 20 (1928) 1327;
4. B.M. Collins, German Patent 2, 302, 658 (Aug. 2, 1973), assigned to Imperial Chemical Ind., Ltd.;
5. French Patent 1, 489, 682 (July 21, 1967), assigned to Imperial Chemical, Ltd.;