Star polymer self-diffusion

Fig. 7. Self-diffusion of linear (open symbols) and three-armed star (filled symbols) polystyrenes (squares) and polybutadienes (circles) in CC14 extrapolated to infinite dilution, as function of polymer molecular weight (Ref. 53>, with permission).

Figure 37 Relative zero-shear viscosity (normalized to the solvent tis) as a function of the effective volume fraction

The result is that diffusion in branched-chain polymers is much slower than in linear chains. For rings, diffusion is even more sluggish, because the ring is forced to collapse into a quasihnear conformation in order to have center-of-mass motion. Since many commercial polymers are branched or star-shaped, the self-diffusion of the polymer is correspondingly decreased, and the melt viscosity increased. 

V.4. Effects of Configuration and Entanglement We also demonstrated the effect of configuration on the dynamic behavior of semidilute polymer solutions. Different results have been obtained by adding to the matrix a 4-arm star polystyrene SPS4 which was comparable with the linear test chain LPS2 in number and size. First, the self-diffusion (the slow mode) became invisible (disappeared). Second, the cooperative diffusion became faster. 

In the case of star polymers as test chains, the more the number of arms, the smaller the possibility for stars to be detached from the matrix once they are attached to the matrix over much longer periods. Even though star test chains are smaller, their motions are still hindered by other entangled polymer coils. If most star test chains participate in the entanglement, the amount of "free" stars is too small to be detected. So the CONTIN analysis did not show two modes for LPS84, but we do not want to deny the possible existence of self-diffusion of star test chains because I I of LPS84 evidently deviated from the single exponential decay. 

Cell, C. B., Graessley, W. W., Efstratiadis, V., Pitsikalis, M., Hadjichristidis, N. Viscoelasticity and self-diffusion in melts of entangled asymmetric star polymers./. Polym Sci., B, Polym Phys. (1997) 35, pp. 1943-1954... 

Frischknecht, A. L., Milner, S. T. Self-diffusion with dynamic dilution in star polymer melts. 

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