OLIGOMERIZATION PROCESS DURING THE INTERCALATION OF ETHYLENE IN CSC24

We present a study on the intercalation Of C2H4 in CSC24. Isotherms of intercalation of ethylene in CSC24 have been established in the range 194 to 323 K and two plateaux have been identified at 1.1 and 2.1 C2H4/24 C. By X ray diffraction at 194 K, the structures corresponding to these plateaux have been identified. The structure of the first is a mixture of two structures, a second-stage ternary and a first-stage binary, and that of the second, obtained by consuming both previous phases, is a pure first-stage ternary. Such a process has already been observed in several organic molecule-alkali metal-graphite systems (THF-CSC24, n-alkanes-CsC24, etc.). However, the peculiar behavior of the C2H4-CSC24 system lies in the ability of ethylene to be oligomerized inside the host material. The conditions of oligomerization depend on temperature: at 233 K, molecules are reversibly intercalated in CSC24, whereas at room temperature the reaction is irreversible because of the formation of large molecules. By calorimetric measurement at 288 K (the temperature where it is only possible to reach the first plateau) we have identified two peaks, the first one corresponding to the heat of intercalation and the second one (appearing later) to the heat of the oligomerization reaction.