Slow Dielectric Relaxation of cis-Polyisoprene near the Glass Transition Temperature

Dielectric measurements were carried out on undiluted cis -polyisoprene (PI) over a wide frequency range from 10 -4 to 10 5 Hz around the glass transition temperature T g (=200 K). The data indicate that the dielectric loss curves including both the normal and segmental mode processes are superposable in the range above 230 K ( T g + 30 K). Below 230 K, the time−temperature superposition is not applicable to the whole loss curve. The ratio of the relaxation times of the normal and segmental modes is constant above 230 K but decreases below 230 K with decreasing temperature.