[0176] in which R and R???, which may be identical or different, are chosen from saturated and unsaturated, linear and branched alkyl radicals comprising from 10 to 30 carbon atoms and such as from 14 to 24 carbon atoms, R and R??? being chosen such that the compound of formula (I) is solid at a temperature of less than or equal to approximately 30??? C. For example, R and R??? are each a stearyl