A new class of water-soluble, amphiphilic star block copolymers with a large number of arms was prepared by sequential atom transfer radical polymerization (ATRP) of n-butyl methacrylate (BMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA). As the macroinitiator for the ATRP, a 2-bromoisobutyric acid functionalized fourth-generation hyperbranched polyester (Boltorn H40) was used, which allowed the preparation of star polymers that contained on average 20 diblock copolymer arms. The synthetic concept was validated by AFM experiments, which allowed direct visualization of single molecules of the multiarm star block copolymers. DSC and SAXS experiments on bulk samples suggested a microphase-separated structure, in agreement with the core−shell architecture of the polymers. SAXS experiments on aqueous solutions indicated that the star block copolymers can be regarded as unimolecular micelles composed of a PBMA core and a diffuse PPEGMA corona. The ability of the polymers to encapsulate and release hydrophobic guests was evaluated using 1H NMR spectroscopy. In dilute aqueous solution, these polymers act as unimolecular containers that can be loaded with up to 27 wt % hydrophobic guest molecules.

Cover: Schematic representation of an amphiphilic multi‐arm star‐block copolymer based on a hyperbranched polymer core. The copolymer was shown to be able to encapsulate and disperse significant loadings of volatile hydrophobic fragrances in aqueous media. Further details can be found in the Full Paper by C. Ternat, G. Kreutzer, C. J. G. Plummer, T. Q. Nguyen, A. Herrmann, L. Ouali, H. Sommer, W. Fieber, M. I. Velazco, H.‐A. Klok, and J.‐A. E. Månson* on page 131.

Self-diffusion NMR spectroscopy and relaxometry have been employed to study fragrance encapsulation in water-soluble, amphiphilic star block copolymers. Diffusion coefficients of four different fragrance molecules in the free form and in the presence of the polymer have been determined and used to calculate the effective degree of encapsulation. In dilute aqueous solutions between 65% and 99% of the guest molecules are trapped inside the polymer. The degree of encapsulation depends on the hydrophobicity of the guest molecule, expressed by the octanol/water partitioning coefficient (log P OW), where high log P OW molecules are nearly quantitatively dissolved in the polymer. The fragrance molecules are mainly located in the hydrophobic core of the polymer, which is tightly packed, whereas the hydrophilic shell is flexible and takes up only a small percentage. Proton longitudinal (T 1) and transverse (T 2) relaxation times of the fragrance molecules are significantly reduced in the presence of the polymer indicating slower rotational correlation times due to microsolubilization in the hydrophobic core.

Graft copolymers of bacterial polyesters were prepared by direct condensation of poly(3‐hydroxyoctanoate‐co‐9‐carboxy‐3‐hydroxydecanoate) (PHOD) and poly(ethylene glycol) (PEG) or poly(lactic acid) (PLA). Nanoparticles from PHO, PHOD, PHOD‐g‐PEG, and PHOD‐g‐PLA were obtained by solvent displacement without stabilizer, and their stability in different aqueous media with different salt concentrations were studied. The results showed that the presence of hydrophilic PEG on the particle surface prevents the aggregation promotion by salts in aqueous solution. PHOD‐g‐PEG appears to be a promising candidate for site‐specific drug delivery systems.

Novel amphiphilic multi‐arm star‐block copolymers with a hyperbranched core, a hydrophobic inner shell, and a hydrophilic outer shell have been prepared from a commercial hyperbranched polyester macroinitiator by ring‐opening polymerization of ε‐caprolactone, followed by atom transfer radical polymerization of tert‐butyl acrylate (tBuA). Hydrolysis of the tert‐butyl groups was then used to convert the poly(tBuA) blocks to poly(acrylic acid), resulting in stable amphiphilic core‐shell structures with significantly higher degrees of functionality than reported so far in the literature. A strong correlation between the maximum concentration of selected hydrophobic guest molecules and the concentration of amphiphilic star‐block copolymer in aqueous solution was observed by 1H NMR, demonstrating the capacity of these copolymers to encapsulate and disperse significant loadings (up to about 27 wt.‐%) of volatile hydrophobic molecules such as fragrances in water.magnified image

Amphiphilic multiarm star-block copolymers with a hydrophobic inner and a hydrophilic outer shell have been used to encapsulate hydrophobic bioactive volatiles in aqueous media under realistic application conditions. The release rates of the bioactive compounds have been investigated for a series of fragrances by thermogravimetry and dynamic headspace analysis. An increasing amount of ethanol present in an aqueous solution linearly reduces the long-lastingness of the fragrance evaporation, which seems to particularly affect nonencapsulated fragrances. An improved controlled release effect is also obtained in the presence of surfactants, where a boosting effect was observed for the fragrance evaporation. Amphiphilic core−shell structures based on hyperbranched polymers were thus found to be suitable delivery systems for the controlled release of bioactive volatiles under typical application conditions. The fundamental understanding of the parameters influencing the release of bioactive compounds is of major interest for the development of tailor-made core−shell structures as efficient delivery systems in various areas of life-science research.

No abstract