High-Temperature dispersion zones in cross-linked natural rubber

The complex dielectric constant of natural rubber samples cross-linked by sulfur and dicumyl peroxide has been measured over a frequency range from 1.5 to 3.0 × 10⁵ cps by the bridge method and from 3.0 to 1.0 × 10⁴ cps by the relaxation method. Two dispersion peaks were detected which lay in the measured frequency range at temperatures above the main dispersion zone. Temperature and cross-link density-dependent shift of these peaks were studied and compared with the results obtained by Ferry et al. from complex compliance measurements performed on analogous systems.