1. U.K. Pat. 2 053 915 (1981) to W.J. Ball and D.G. Stewart (B.P.).
2. Eur. Pat. 29 723 (1981) to M.T. Barlow (B.P.).
3. Eur. Pat. 51 859 (1982) to B. Cornils, C.D. Frohning, G. Diethaus, E. Wiebus and H. Bahnnann (Ruhrchemie).
4. Eur. Pat. 27 000 (1981) to G. Doyle (Exxon).
5. Eur. Pat. 30 434 (1981) to G. Doyle (Exxon).