Self-diffusivity in block copolymer solutions. 2. A₂B simple grafts

The composition and concentration dependencies of the self-diffusion coefficients for a series of miktoarm star block copolymers of the A₂B type in solutions in a common good solvent have been investigated by pulsed-field-gradient nuclear magnetic resonance; the graft copolymers are composed of A = polyisoprene and B = polystyrene, where the B block was attached either in the middle of the A block (τ = 0.5) or at a position with τ = 0.25. The dependence of the diffusion coefficients on concentration, in both A₂B graft copolymers and AB diblock copolymers, can be collapsed onto a master curve with a proposed scaling procedure which takes into account the difference in the entanglement characteristics of the parent homopolymers and the different radii of gyration of stars vs linear polymers. The exponential slowing down of the diffusivities expected for star molecules was not observed due to the only moderately high molecular weights and concentrations.