On the structure of polyurethane hard segments based on MDI and butanediol‐1,4: X‐ray diffraction analysis of oriented elastomers and of single crystals of a model compound

Single‐crystal x‐ray diffraction analysis is performed on a model compound (bisurethane of diphenylmethane‐4–monoisocyanate and butanediol‐1,4) for the thermoplastic polyurethane (TPU) hard segment formed from diphenylmethane‐4,4′‐diisocyanate and butanediol‐1,4. The resulting structure is compared to structure models of corresponding TPU hard segments, especially to the structure proposed by Blackwell and Ross. Our results confirm this structure model showing a planar zigzag of the (CH 2 ) 4 group and planar hydrogen bonding between the urethane groups of adjacent molecules. X‐ray diffraction analyses of polymeric TPU hard segments and of TPU elastomers with noncrystallizing soft segments lead to a revision of the dimensions of the proposed lattice cell, resulting in a more plausible value of 1.3226g/cm 3 for the crystal density.