Component dynamics in polyisoprene/polyvinylethylene blends well above T_g

¹³C and ²H NMR relaxation time measurements were performed on low molecular weight blends of polyisoprene (M_n = 1350 g/mol) and deuterated polyvinylethylene (1,2-polybutadiene; M_n = 2350 g/mol) in order to extract the segmental correlation times for each component. A wide range of temperatures (295-405 K) and several compositions (PI/dPVE: 100/0, 70/30, 50/50, 30/70, and 0/100) were investigated. At high temperatures, dPVE dynamics are 6 times slower than PI dynamics even after considering self-concentration effects. This intrinsic mobility difference is in quantitative agreement with measurements on each chain individually as a dilute component in a common solvent, suggesting a purely intramolecular origin. The reported correlation times at various compositions fit together smoothly with those obtained by Kornfield and co-workers near T_g, thus providing a unified data set for testing models. One model based on local composition fluctuations captures some qualitative features of the experimental data while failing to describe others.