The effects of the addition of organically modified nanoparticles on molecular dynamics, and subsequently, crystallization parameters were investigated using temperature modulated differential scanning calorimetry, dynamic mechanical analysis, and rheological measurements. Cold crystallization was observed to occur, at higher temperatures compared to the pure sample, due to the formation of topological constraints and the increase of the rigid fraction of amorphous chains, trapped in the polymer-particle interphase. It was also found that in the nanocomposites, the competition between the heterogeneous nucleating role of the nanoparticles and the restricted morphology effect on crystallization kinetics depends on devitrification of the rigid amorphous chains, at the isothermal crystallization temperature, and during nonisothermal crystallization. It was illustrated that the fraction of rigid amorphous chains, extended at the crystal-amorphous interphase, was enhanced by the increase of the overall crystallization rate. Moreover, the internal structure of the crystalline domains was revealed through small angle X-ray scattering. A correlation function was applied to SAXS data to estimate the long period and the thickness of alternatively stacked lamellae. It was demonstrated that the long period depends on the overall crystallization rate, which was found to be influenced by nanoparticle content. In contrast, the lamellae thickness did not show a noticeable variation with the addition of the nanoparticles. POLYM. ENG. SCI., 55:1310-1320, 2015. (c) 2015 Society of Plastics Engineers