Chain trapping in diblock copolymers near the ordering transition

The mean-square displacement, ⟨Δ r 2 ⟩, of very high molecular weight diblock copolymers in solutions near the disorder-to-order transition is investigated by pulsed-field-gradient NMR. The thermodynamic potential influencing the motion leads to a time-in de pend ent ⟨Δ r 2 ⟩ at short times followed by free-diffusional behavior. The plateau is attributed to a trapping of the copolymer chains at the "quasi-interfaces" formed by slow composition fluctuations.