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