The linear dynamic viscoelastic properties and non-linear transient theology of polycarbonate (PC)/clay nanocomposites were investigated at temperatures ranging from 240 to 280degreesC. For the study, nanocomposites of PC and natural montmorillonite (Cloisite Na+) or chemically modified clay (Cloisite 3013) were prepared by melt blending in a twin-screw extruder. Cloisite 30B is a natural montmorillonite modified with methyl, tallow, bis-2-hydroxyethyl, quaternary ammonium chloride (MT2EtOH). In both PC/Cloisite Na+ and PC/Cloisite 30B nanocomposites the concentration of clay was varied from 2.3 to 4.3 wt%. In situ Fourier transform infrared (FTIR) spectroscopy results show that at temperatures ranging from 30 to 280degreesC the carbonyl groups in PC and the hydroxyl groups in MT2EtOH of Cloisite 30B in PC/Cloisite 30B nanocomposites formed hydrogen bonds, while no evidence of hydrogen bonding was observed in the PC/Cloisite Na+ nanocomposites. There are no discernible sharp reflections in the X-ray diffraction (XRD) patterns of PC/Cloisite 30B nanocomposites, after Cloisite 30B having the d(001), spacing of 1.85 rim was mixed with PC, whereas the d(001), spacing changes little (1.17 nm) before and after the mixing of Cloisite Na+ to PC. Transmission electron microcopy (TEM) images show that organoclay platelets are well dispersed in PC/Cloisite 30B nanocomposites, while the untreated clay platelets are poorly dispersed in PC/Cloisite Na+ nanocomposites. The observed differences in XRD patterns and TEM images between the two nanocomposite systems are explained by in situ FTIR spectroscopy. The results of theological measurements (linear dynamic viscoelasticity, non-linear transient shear flow, and steady-state shear flow) support the conclusions drawn from the results of XRD, TEM, and FTIR spectroscopy. (C) 2003 Elsevier Science Ltd. All rights reserved.