Self-diffusivity of diblock copolymers in solutions in neutral good solvents

The composition, f, and concentration, phi, dependence of the self-diffusion coefficients of diblock copolymers in solutions in a common goad solvent have been investigated by pulsed-field-gradient nuclear magnetic 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 investigation on toluene solutions for a series of poly(styrene-b-isoprene) diblocks, possessing almost similar molecular weights and compositions ranging from 0.18 to 0.74, showed that the dependence of the diffusivity on diblock composition f conforms with the progressive transition from the Rouse to the entanglement regime at different concentrations due to the different critical molecular weights for entanglement of the patent homopolymers. The same idea can account for the diblock composition dependence of the self-diffusivity for poly(styrene-b-butadiene) diblocks. Moreover, the self-diffusivities For three poly(styrene-b-methyl methacrylate) diblocks in toluene are insensitive to copolymer composition (0.35 to 0.69) in accord with the very similar entanglement characteristics of the two blocks.