The effect of rigid poly(styrene-co-acrylonitrile) nano and micro-particles on the dynamic heterogeneity of poly(butyl acrylate-co-methyl methacrylate) (BM) matrices and the ultrasound attenuation in the corresponding composite systems were studied. The loss of local segmental mobility in the matrix chains located within an interfacial layer around the rigid nanoparticles and its consequent influence on the macroscopic response of the filled copolymers was investigated by dynamic mechanical (DMA), differential scanning calorimetry (DSC), and solid-state NMR methods. Upon comparison with the neat copolymers, no significant changes in the peak temperature and width of the matrix glass transition were observed in the DMA and the DSC data of the composites. The H-1 transverse relaxation and dipolar filtering experiments of the matrix phase gave similar results for both the neat copolymers and the composite samples. In alignment with the NMR results, the weight fraction of the vitrified chains segments, obtained from heat capacity step at T-g, was found to be only around 2% of the matrix phase. The insensitivity of the applied experimental techniques to the presence of the interfacial layer was also verified by calculating the thickness and weight fraction of this layer in a weakly interacting nanocomposite. Furthermore ultrasound attenuation of the neat and filled BM copolymers was described in terms of viscoelastic loss in the matrix phase and contributions from wave scattering from the rigid particles. (c) 2013 Elsevier Ltd. All rights reserved.