Structural studies on urethane elastomers

A number of techniques have been used to study structural organization and transitions in polyether- and polyester-based urethane elastomers. Scanning thermal methods reveal three characteristic transitions common to samples of varying composition, namely, the major glass transition and two higher transitions believed due to disruption of different types of hydrogen bonding. Other transitions are assigned to melting of ester and of urethane crystallites. Light-scattering measurements on turbid polyether-based samples indicate both isotropic and anisotropic contributions to scattered intensity, the latter reflecting structural ordering on a small scale. X-Ray diffraction studies of stress-induced crystallization in the polyetherbased elastomer show reflections attributed to crystallites of polyether segments. It is concluded that separation into a domain structure occurs in both types of elastomers, but to a higher degree in the polyether-based polymers than in the polyester-based polymers, possibly due to restrictions in the latter imposed by interaction of the ester and urethane groups.