{HEAD ~ Cyclic lactones} having a closed ring structure containing {TAIL ~ six members} can also be employed, if desired, such as lactide or glycolide 
{ HEAD ~ Cyclic lactones } having a closed ring structure containing { TAIL ~ six members } can also be employed , if desired , such as lactide or glycolide
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH