aryl radical, {TAIL ~ Y} is {HEAD ~ a monovalent aliphatic or cycloaliphatic group} selected from ##STR17## R1 and R4 are selected from hydrogen and C.sub 
aryl radical , { TAIL ~ Y } is { HEAD ~ a monovalent aliphatic or cycloaliphatic group } selected from # # STR17 # # R1 and R4 are selected from hydrogen and C.sub
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH