The pressure-volume-temperature (PVT) dependencies of polyamide-6 and its nanocomposites (polymeric nanocomposites) were measured at temperatures T = 300-600 K and pressures P = 0.1-190 MPa, thus spanning the range of molten and "solid" phases. The Simha-Somcynsky (S-S) cell-hole equation of state (EOS) was used for describing the molten region. At T-g(P) <= T <= T-m(P), the "solid" phase is a mixture of the liquid polyamide-6 with dispersion of crystals. Accordingly, the PVT behavior in this region was described as a combination of the S-S EOS for the liquid phase and the Midha-Nanda-Simha-Jain (MNSJ) EOS for the crystalline one. These two theories based on different models yielded two sets of the characteristic reducing parameters, P-*, T-*, V-* and the segmental molecular weight, M-s. Incorporation of 2 and 5 wt % clay increased P-* and reduced T-* and V-*, but the effects were small. Fitting the combination of S-S and MNSJ EOS' to isobaric "solid" phase data yielded the total crystallinity, X-cryst, and the correcting excess specific volume, Delta V-m,V-c. Both parameters were sensitive to pressure, P, and the clay content, w-the former increased with P and w, whereas the latter decreased. The raw PVT data were numerically differentiated to obtain the thermal expansion and compressibility coefficients, alpha and kappa, respectively. At T < T-m, addition of clay reduced their relative magnitude, whereas at T > T-m, the opposite effect was observed, most likely owing to the excess of intercalant in the polymeric nanocomposites samples. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 966-980, 2009