1 H-NMR spectra of neat ATV, neat polymer or ATV formulations at varying A-pBuOzi-A/ATV ratio were recorded. In DMSOd 6 , all signals related to ATV were clearly visible with expected intensities (Figure ; black spectrum; for enlarged ATV and A-pBuOzi-A spectra, the reader is referred to Figure and S5, respectively). In contrast, when solubilized with A-pBuOzi-A, 1 H-NMR signals of ATV were either strongly attenuated and broadened (A-pBuOzi-A/ATV ≤ 10/0.9) or could not be detected anymore (A-pBuOzi-A/ATV > 10/0.9) in D 2 O (Figure ; enlarged spectra). A similar disappearance of 1 H-NMR signals was already observed for A-pPrOzi-A/CUR formulations. Systems which are hindered in their mobility are predestinated for short transverse relaxation times T 2 causing a broadening or complete disappearance of certain signals. Therefore, the disappearance of the 1 H-NMR signals indicates a strong decrease in molecular mobility of ATV incorporated into the hydrophobic core of A-pBuOzi-A even at low loading. Furthermore, the signals of the butyl sidechain of the hydrophobic block are clearly affected (Figure ). Notably, the signal attributed to the methyl group in the sidechain of pBuOzi (signal V) splits up. Besides the initial triplet, a second, much broader signal was observed at lower chemical shift. Similarly, but somewhat less pronounced, signals III and IV shift and became increasingly attenuated with increasing ATV loading. This decrease again is intuitive for a hindered mobility due to interactions of ATV with the hydrophobic block of A-pBuOzi-A. In contrast, the signals related to the hydrophilic shell (Figure I,II) appear entirely unaffected even at the highest investigated drug loading. This results in a decreased ratio of the integrals of the methyl group of pBuOzi (core, signal V) with respect to the methyl sidechain of pMeOx (shell, signal II) with increasing ATV-loading (Figure ). The more or less linear decrease of the ratio as well as the largely unaffected signals related to the hydrophilic shell are somehow surprising considering the large change in particle size at higher ATV-loadings observed by DLS (Figure ). Also, we previously investigated A-pPrOzi-A/CUR formulations by solution and solid state NMR and found clear evidence for drug-polymer interactions in the hydrophilic pMeOx block. The lack of interaction of ATV with the pMeOx may therefore be responsible for the limited LC compared to CUR or PTX nanoformulations which exhibit LC of ≥ 50 wt.%. For reference, interactions between encapsulated ATV and the hydrophobic part of the polymeric drug carrier were observed previously for PLA-PEG-PLA-loaded ATV by FT-IR analysis.