Dynamic Heterogeneity and Density Scaling in 1,4-Polyisoprene

摘要: Dielectric relaxation times were measured for 1,4-polyisoprenes (PI) of different molecular weight. From the data, number dynamically correlated segments, Nc, was calculated using an approximation to dynamic susceptibility. Nc increases with approach glass transition in usual fashionandalsoincreaseswithincreasingmolecularweightofthePI.Thelattereffectisascribedtothelossof configurational mobility conferred by chain ends. The correlation volume also estimated from calorimetry and,because PI hasadielectrically active normal mode,from theintersection oftheextrapolated segmentalandnormalmoderelaxationtimes.Thethreemethodsyieldconsistentresults,althoughthelasthas large uncertainty due ambiguous connection between lengths and volumes. Using equation state polymers, dependence on scaling variable TV γ , where V is specific a material constant, calculated. For lowest weight PI, there small difference segmental modes. exponent marginally smaller lower sample, suggesting, contrast behavior other that becomes weaker decreasing