|Title||Miscible polyisoprene/polystyrene blends: Distinct segmental dynamics but homogeneous terminal dynamics|
|Publication Type||Journal Article|
|Year of Publication||2005|
|Authors||He, Y. Y., T. R. Lutz, M. D. Ediger, M. Pitsikalis, N. Hadjichristidis, and E. A. von Meerwall|
|Keywords||ATACTIC POLYPROPYLENE MELTS, COMPONENT DYNAMICS, CONCENTRATION FLUCTUATIONS, GLASS-TRANSITION TEMPERATURES, HIGH-MOLECULAR-WEIGHT, ISOPRENE TETRABLOCK COPOLYMERS, local dynamics, NMR DIFFUSION MEASUREMENTS, NUCLEAR-MAGNETIC-RESONANCE, POLYMER BLENDS|
The segmental and terminal dynamics of the individual components in miscible blends of polyisoprene (PI) and polystyrene (d(3)PS) were characterized over a wide temperature range. Though the system has a large positive Flory-Huggins interaction parameter chi similar to 0.1, it is miscible in the temperature range of study due to low molecular weight. C-13 and H-2 NMR relaxation measurements were performed to extract the segmental relaxation times. Pulse-gradient spin-echo NMR was used to determine the center-of-mass diffusion coefficients. Though the segmental dynamics of PI and PS components differ by more than 2 decades at T-g + 50 K in the blends, their terminal dynamics (in terms of monomeric friction coefficients) are essentially identical. We know of no other system with this behavior. The distinct component segmental dynamics can be reasonably interpreted by the Lodge/McLeish model. The unusual homogeneous terminal dynamics may be due to a large thermodynamic barrier to diffusion in this system. The monomeric friction coefficients are well reproduced by the Gordon-Taylor mixing rule.