RESTRICTED DIFFUSION IN THE REGIME OF THE ORDER-TO-DISORDER TRANSITION IN DIBLOCK COPOLYMERS - A FIELD GRADIENT NMR-STUDY

The self-diffusion of diblock copolymers of polystyrene/cis-1,4-isopre ne and polyisoprene homopolymers is studied using field gradient nucle ar magnetic resonance. The block copolymers are shown to go through th eir order-to-disorder transition (ODT) at experimentally accessible te mperatures. Their phase state is determined using small-angle X-ray sc attering. Diffusion in the ordered, lamellar phase is found to be spat ially restricted. Fast motion is possible along the lamellae and withi n a grain. The crossing over the enthalpic barriers between styrene an d isoprene domains takes place on a much longer time scale. The ODT do es not lead to an abrupt crossover to unrestricted diffusion. Local or der remains even above the ODT, and the barriers disappear only gradua lly.