DIELECTRIC BEHAVIOR OF CARBOXYLATO-TELECHELIC AND SULPHONATO-TELECHELIC POLYDIENES

Linear polydiene chains selectively end-capped by an ionic group have been investigated by dielectric spectroscopy in relation to both polydispersity and the glass transition temperature (T(g)) of the polymer and nature of the dipolar end groups. An alpha-relaxation associated with the micro-Brownian motion of chain segments is systematically observed. When the chain length distribution is broad the structure of the alpha-relaxation is complex and reflects an incomplete segregation of ionic and non-ionic components. The thermal dissociation of the ionic multiplets allows unpaired carboxylate groups to be released (SIGMA phenomenon); it is observed as a large relaxation process when it occurs at a temperature much higher than T(g) (e.g. 100-degrees-C) and when carboxylate end groups are associated with alkaline cations (excluding alkaline earth cations). When the glass transition of the matrix and the thermal dissociation of the multiplets interfere, the situation is more complex: the alpha-relaxation is observed at a temperature lower than expected; and the SIGMA phenomenon is no longer detected (in the usually investigated temperature range) although an unexplained low amplitude relaxation is noted beyond the alpha-relaxation.