Phase selective, ultrahigh loading of nanoparticles into target domains of block copolymer composites was achieved by blending the block copolymer hosts with small molecule additives that exhibit strong interactions with one of the polymer chain segments and with the nanoparticle ligands via hydrogen bonding. The addition of d-tartaric acid to poly(ethylene oxide-block-tert-butyl acrylate) (PEO-b-PtBA) enabled the loading of more than 150 wt % of 4-hydroxythiophenol-functionalized Au nanoparticles relative to the mass of the target domain (PEO + tartaric acid), which corresponds to greater than 40 wt % Au by mass of the resulting well-ordered composite as measured by thermal gravimetric analysis. The additive, tartaric acid, performs three important roles. First, as evidenced by small-angle X-ray scattering, it significantly increases the segregation strength of the block copolymer via selective interaction with the hydrophilic PEO block. Second, it expands the PEO block and enhances the number and strength of enthalpically favorable interactions between the nanoparticle ligands and the host domain. Finally, it mitigates entropic penalties associated with NP incorporation within the target domain of the BCP composite. This general approach provides a simple, efficient pathway for the fabrication of well-ordered organic/nanoparticle hybrid materials with the NP core content over 40 wt %.