The phase behavior of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends with amorphous polymers with different degrees of aromaticity has been investigated by differential scanning calorimetry (DSC) and small-angle neutron scattering (SANS). The polymers investigated are the homologous series of polystyrene (PS), poly(2-vinyl-naphthalene) (P2VN), and poly(9-vinyl-phenanthrene) (P9VPh). The DSC results show that the miscibility of PCBM in these polymers increases nonlinearly from 16.5 wt % in PS, 57.0 wt % in P2VN, and 74.9 wt % in P9VPh. The SANS results show that at all concentrations of PCBM, the blends are composed of two mixed phases. Analysis shows that the phase dimensions remain largely independent of PCBM content, but there is a strong dependence of the PCBM concentration difference in the two phases with increasing PCBM content. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016