Poly(methyl methacrylate) (PMMA)-clay nanocomposites (PCN) were prepared with PMMA/clay concentrates and POP-diamines modified clay via melt blending. Partially exfoliated clay layers were uniformly dispersed in the nanocomposites as evidenced from XRD study. The subglass beta relaxation and the segmental a relaxation were observed from the dynamic mechanical thermal analysis (DMTA). The PCNs at 5 wt% clay level from clay concentrate exhibited significantly higher glass-transition temperatures and dynamic storage moduli relative to the neat PMMA. The confinement effect from the tethering of polymer chain to the clay surface would contribute to such a dramatic difference. In addition to the normal-mode relaxations, the alpha beta-merging process above T-g and the subglass interfacial polarization were detected from the dielectric analysis. Significant increase in dielectric permittivities and dielectric losses due to interfacial polarization and ionic conduction at low frequency were observed for the PCNs. The intensity of the interfacial polarization process increases with the dispersion degree of clay layers and hence the process can be assigned to the space charge polarization of the ionic species in the clay intergalleries. (C) Koninklijke Brill NV, Leiden, 2010