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Structural Studies on Polyurethane Fibers. I. Crystal and Molecular Structures of Aliphatic Polyurethanes from Hexamethylene Diisocyanate and Some Linear Glycols

The molecular and crystal structures of aliphatic polyurethane series –[O–(CH2)m–OCONH–(CH2)6–NHCO–]p– with m=2–6, have been studied by X-ray diffraction methods. Two types of molecular structures have been found. The one (m=3, 5 and type II of m=2) is similiar to the model proposed for γ-phase of polyamides, where the hydrogen bonding requirements between adjacent chains are satisfied by tilting the urethane group planes approximately 30° with respect to the fiber axis causing a shortening of the fiber identity periods. The other (m=4, 6 and type I of m=2) is similar to the α-phase of polyamides, where the molecular chains have planar zigzag conformation. These structures are well confirmed by the comparison of the observed and calculated intensities of X-ray diffraction spots.