Local Order and Chain Dynamics in Molten Polymer Blocks Revealed by Proton Double-Quantum NMR

Abstract

High-resolution proton double-quantum (DQ) magic-angle spinning (MAS) NMR is used as a new technique that is capable of revealing complex motional processes in entangled polymer melts. Theoretical analysis shows the connection 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 observed for polybutadiene (PB). Here, the influence of rigid confinements represented by immobile moieties attached to one or both chain ends of the PB block on chain dynamics and ordering are investigated. Symmetric poly(styrene- 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 more than a factor of 2 for block copolymers compared to homopolymers. Furthermore, on account of the chemical constraints imposed on the PB block, the lack of the motional regime that involves diffusive reptation motion is experimentally confirmed. Correspondingly, the scaling law pattern differs qualitatively from those observed for PB homopolymers.