prov:value
| - The hemispherands useful in the practice of this invention are represented by the structure: ##STR5## wherein X1, X2, X3 and X4 are independently alkyl, preferably of 1 to 5 carbon atoms (substitued or unsubstituted, e.g. methyl, ethyl, propyl, isopropyl, t-butyl, chloromethyl, benzyl etc.); or alkenyl, preferably of 2 to 5 carbon atoms (substituted or unsubstituted, e.g. vinyl, allyl, 1-propenyl,
|