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