[-NH.CO.O-]

from The Collaborative International Dictionary of English v.0.48
Polyurethane \Pol"y*ur`eth*ane\, n. (Chem.)
   any polymer containing {[-NH.CO.O-]} linkages; such polymers
   are much used as the basis of light but rigid foams for
   packaging (

   {polyurethane foam}) and for hard coatings, as on floors.
      [PJC]
    

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