posted on 2005-07-12, 00:00authored byYiyong He, T. R. Lutz, M. D. Ediger, Marinos Pitsikalis, Nikos Hadjichristidis, Ernst D. von Meerwall
The segmental and terminal dynamics of the individual components in miscible blends of
polyisoprene (PI) and polystyrene (d3PS) were characterized over a wide temperature range. Though the
system has a large positive Flory−Huggins interaction parameter χ ∼ 0.1, it is miscible in the temperature
range of study due to low molecular weight. 13C and 2H 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 Tg + 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.