Dielectric study of the alpha-relaxation process evolution during polyurethane networks formation

Quenched systems corresponding to different reaction extents of polyurethan e (PU) network formation have been studied using broadband dielectric spect roscopy in order to apprehend the evolution of alpha-relaxation during gel formation. Three PU systems based on poly(oxypropylene) triol of molar mass 260, 700 and 6000 g/mol. have been investigated. While for the pure triols the distribution and temperature dependence of relaxation times are found to be similar, their evolution with connectivity in PU systems depends on m olar mass of the triol used. This has been interpreted in terms of relative influence and transformation of active dipoles as a consequence of reactio n and evidenced by the appearance of a new dynamic associated to new active dipoles. (C) 2000 Elsevier Science Ltd. All rights reserved.