DIELECTRIC-RELAXATION OF BALL-LIKE LABELS IN POLYISOPRENE

Ball-like molecules with strong dipoles (labels) were mixed with synth etic polyisoprene (IR305) in low concentrations (<1%) and measured die lectrically in the frequency range 10(-2)-10(7) Hz and the temperature range - 70-0 degrees C (glass relaxation region). Calorimetric measur ements showed that this type of label has a plasticizing effect on the polymeric matrix. The dielectric measurements showed that these ball- like molecules relax through cooperative rotations with the polymeric segments and at the same relaxation frequency. In addition, the label molecules showed a high-frequency local relaxation process. The relaxa tion strength ratio of the local process (X(local)) tolaxation strengt h of the label was found to be dependent on the volume as well as on t he shape of the label. A comparison between the relaxation behaviors o f the ball- and rod-like molecules, having the same volume, showed tha t the length of the label is also an important parameter for the deter mination of the local contribution as well as of the cooperative relax ation mechanism of the label. The label relaxation process is discusse d in relation to the molecular packing of the host polymer.