Critical Effect of Segmental Dynamics in Polybutadiene/Clay Nanocomposites Characterized by Solid State H NMR Spectroscopy

The segmental dynamics of rigid, intermediate, and mobile molecular components in carboxyl terminated polybutadiene (CTPB)/ organo−clay (C18−clay) systems was characterized by fully refocused H NMR FID. In addition, H DQ NMR experiments allowed semiquantitative monitoring of changes in segmental dynamics near the interface. Both methods suggest a critical concentration of 60 wt % CTPB, indicating a saturation effect for the surface-adsorbed polymer. While the critical concentration value of a polymer/clay system can be measured in several ways, this is its first direct evidence at the molecular scale. The polymer−clay interaction is found to profoundly change with the removal of the CTPB end group or the organic modifier on the clay surface thus impacting the polymer segmental dynamics near the clay surface. In C18−clay by itself, with increasing temperature, the dynamic behavior of surface modifier changes from homogeneous to heterogeneous, on the basis of which the nonreversible exfoliation process of CTPB/clay nanocomposites could be explained at the molecular level. Based on the H NMR results, a tentative model was proposed to illustrate the evolution of the structure and segmental dynamics in CTPB/organo−clay nanocomposites.