In this research, hydroxyapatite nanoparticles sparsely coated with tethered poly(ethylene oxide) (PEO) chains were added to a bulk PEO matrix of greater molecular weight. The nanoparticles were found to be dispersed homogeneously when the particle concentration was high. Two different low-aspect ratio shaped particles were used, spherical and needle, and had similar dispersion behavior in this matrix. Characterization results indicated that the homogeneous dispersion achieved here at higher particle loadings was a kinetically trapped condition and an interfacial zone had developed at the grafted polymer/matrix polymer interface. Additionally at a critical nanoparticle loading related to specific values of the nanoparticle surface area and interparticle spacing, the crystallite size and amount of crystallinity in the PEO matrix began to decrease as opposed to the level of nanoparticle dispersion. Overall, these results provide a strategy for incorporating relatively high loadings of nanoparticles into these matrices without large scale phase segregation. (C) 2012 Elsevier Ltd. All rights reserved.