Local order and chain dynamics in molten polymer blocks revealed by protondouble-quantum NMR

High-resolution proton double-quantum (DQ) magic-angle spinning (MAS) NMR i s used as a new technique that is capable of revealing complex motional pro cesses in entangled polymer melts. Theoretical analysis shows the connectio n of quantities relating anisotropic polymer dynamics to data obtained from our DQ-MAS NMR experiment. With this technique, dynamic chain ordering as well as scaling laws consistent with the reptation model was previously obs erved for polybutadiene (PB). Here, the influence of rigid confinements rep resented by immobile moieties attached to one or both chain ends of the PB block on chain dynamics and ordering are investigated. Symmetric poly(styre ne-b-butadiene) diblock copolymers (PS-b-PB) with varying molecular weights are examined as systems with one anchored chain end. As materials with two tethered chain ends PS-b-PB-b-PS triblock copolymers are studied. In these systems, the effects of rigid confinements on the polymer dynamics in the melt are analyzed. We find that dynamic order parameters are increased by m ore than a factor of 2 for block copolymers compared to homopolymers. Furth ermore, on account of the chemical constraints imposed on the PB block, the lack of the motional regime that involves diffusive reptation motion is ex perimentally confirmed. Correspondingly, the scaling law pattern differs qu alitatively from those observed for PB homopolymers.