Chemical structure and physical properties in polyester based segmented polyurethanes—I: Dynamic mechanical properties

Nine polyester based segmented polyurethanes and one polyurea have been synthesised, wet spun into fibres and cast into films. Both forms have been found to have melting points and densities strongly dependent on soft segment (polyester) concentration, the films having higher values in each case. Electron microscope studies have revealed the presence of crystallinity within the hard domains. Dynamic mechanical measurements showed several transitions: an α transition above 200° complete in several film samples but incomplete in fibre, an α' transition between 47 and 80° and a β transition in the region of ?20°. The α transitions occurred in the film but not in fibre, the α' transition in the fibre but not the film and the β transition in both. The significances of the transitions are discussed in terms of physical and chemical structure.