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Polycarbonate-based polyurethane (PC-PUs) hybrid materials were obtained by the addition of organically modified bentonite and montmorillonite (1 w/w %). PC-PUs and their nanocomposites were prepared using prepolymerization with two polycarbonate diols (both of Mr ca 1000) differing in chain constitution, hexamethylene-diisocyanate and 1,4-butane diol (chain extender) as starting components. All samples contained the same hard-segment content (30 w/w %). Thermogravimetry coupled with differential scanning calorimetry (TG-DSC) was performed to obtain information about the organoclays addition on the thermal stability of the prepared polyurethane elastomers. The effect of bentonite and montmorillonite nanofillers on the decomposition pattern has been evaluated. By deconvolution of derivative thermogravimetric (DTG) curves, it has been found that the thermal decomposition of polyurethane samples takes place in three overlapping processes. Degradation kinetic parameters (activation energy and reaction order) were calculated on the basis of thermal data obtained at only one heating rate.