NMR evidence for residual dipolar interactions in SBS systems: Influence of a plasticizer on the network structure

Evidence for residual dipolar interactions in the polybutadiene domains of two poly(styrene-butadiene- styrene) block copolymers is shown at temperatures ranging from ambient to 90 degreesC. The two copolymers differ for the presence of a plasticizer, selectively compatible with the polybutadiene blocks. The evidence results from the analysis of H-1 transverse magnetization decays, H-1 pseudo-solid echoes, and C-13 edited H-1 spectra. H-1 transverse magnetization decay data can be interpreted using a simplified network model, which provides the number N of statistical segments between cross-links. The analysis of decays and H-1 pseudo-solid echoes shows that the plasticizer induces a lowering of the entanglement density. These results are consistent with the information obtained from the C-13 edited H-1 spectra.