The composition, f, and concentration, phi, dependence of the self-dif
fusion coefficients of diblock copolymers in solutions in a common goa
d solvent have been investigated by pulsed-field-gradient nuclear magn
etic resonance and photon correlation spectroscopy. The difference in
the entanglement characteristics of the parent homopolymers was found
to be very important in determining the diffusion coefficients. The in
vestigation on toluene solutions for a series of poly(styrene-b-isopre
ne) diblocks, possessing almost similar molecular weights and composit
ions ranging from 0.18 to 0.74, showed that the dependence of the diff
usivity on diblock composition f conforms with the progressive transit
ion from the Rouse to the entanglement regime at different concentrati
ons due to the different critical molecular weights for entanglement o
f the patent homopolymers. The same idea can account for the diblock c
omposition dependence of the self-diffusivity for poly(styrene-b-butad
iene) diblocks. Moreover, the self-diffusivities For three poly(styren
e-b-methyl methacrylate) diblocks in toluene are insensitive to copoly
mer composition (0.35 to 0.69) in accord with the very similar entangl
ement characteristics of the two blocks.