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