Component dynamics in polyisoprene/polyvinylethylene blends well above T-g

C-13 and H-2 NMR relaxation time measurements were performed on low molecul ar weight blends of polyisoprene (M-n = 1350 g/mol) and deuterated polyviny lethylene (1,2-polybutadiene; M-n = 2350 g/mol) in order to extract the seg mental 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, an d 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 measu rements on each chain individually as a dilute component in a common solven t, suggesting a purely intramolecular origin. The reported correlation time s at various compositions fit together smoothly with those obtained by Korn field and co-workers near T,, thus providing a unified data set for resting models. One model based on local composition fluctuations captures some qu alitative features of the experimental data while failing to describe other s.