alkyl radicals, R2 and R3 are ##STR18## or a mixture of ##STR19## where {TAIL ~ R7} and {HEAD ~ R8} are selected from C.sub 
alkyl radicals , R2 and R3 are # # STR18 # # or a mixture of # # STR19 # # where { TAIL ~ R7 } and { HEAD ~ R8 } are selected from C.sub
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH