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