X in {TAIL ~ formula} represents a hydrogen atom, a halogen atom, {HEAD ~ a hydrocarbon group} having 1 to 20 carbon atoms, an alkoxy group or an amido group 
X in { TAIL ~ formula } represents a hydrogen atom , a halogen atom , { HEAD ~ a hydrocarbon group } having 1 to 20 carbon atoms , an alkoxy group or an amido group
OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH 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