SELF-DIFFUSIVITY OF DIBLOCK COPOLYMERS IN SOLUTIONS IN NEUTRAL GOOD SOLVENTS

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.