Physical and chemical network effects in polyurethane elastomers

Abstract

The effects of the physical and chemical networks on the relaxation processes and on the morphology of polyester-based polyurethane elastomers were studied by thermal, thermomechanical, and dielectric methods. Two series of polyester-based polyurethane elastomers were prepared by varying the NCO/OH ratio during the second step of polymerization while the hard segment content was maintained almost constant, at about 30% in the first series and at about 39% in the second. Differential Scanning Calorimetry (DSC), dielectric ac and Thermally Stimulated Depolarization Current (TSDC) measurements and Dynamic Mechanical Analysis show a main relaxation related to the glass transition of the soft parts of the polyurethane copolymers. The results of all the techniques used have shown that the increase of the NCO/OH ratio produces an increase in the glass transition temperature and a more homogeneous morphology. Dielectric ac and TSDC relaxation spectroscopy provided more information about the dynamics of the glass transition.