1. E. Billig (Union Carbide Corp.), European Patent Appl. 28,378 (1981)
2. T. F. Shevels and N. Harris (Davy McKee (Oil & Chemicals) Ltd.), European Patent Appl. 16,285 (1980).
3. E. A. V. Brewester and R. L. Pruett (Union Carbide Corp.), US Patent 4,247,486 (1981).