Solubilisation and Release of Organic Compounds of Different Polarity by Interpolyelectrolyte Complexes Based on Block Copolymer Micelles

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The main aim of this project is to develop well-defined core-shell-corona IPEC micelles and to investigate them with respect to their solubilisation and release properties. For that purpose we start from amphiphilic block copolymers of the poly(alkylacrylate)-b-poly(acrylic acid) (PAlkA-b-PAA) type, which form micelles in aqueous solution and will be synthesised in this project. By addition of a polycation a shell of an interpolyelectrolyte complex (IPEC) is formed to produce copolymer IPEC micelles. As an interesting variation we will employ double-hydrophilic diblock copolymers with a neutral block as polycations. The properties of this shell are controlled by the choice of polycation, and the hydrophobicity of the micellar core via the length of the alkyl chain of the PAlkA. In addition, the size of core and shell will be controlled by the length of the PAlkA block and the amount of the added polycation, respectively. As a first step we will characterise in detail the structure of these IPEC micelles as a function of their molecular building blocks in order to determine systematic correlations between them. Here we will mainly employ scattering techniques and fluorescence measurements. In the second step we will determine the solubilisation capacity for oils of different polarity for differently sized and structured IPEC micelles. Structural changes of the IPEC micelles induced by solubilisation as well as the solubilisation site (core and/or shell) will be determined. From that systematic correlations between the polarities of the oil, micelle core and IPEC shell and the solubilisation site and the resulting structural changes will be deduced. Here we will also use drug molecules as polar solubilisates, which are expected to become solubilized preferentially in the IPEC shell. Having a multi-compartment systems we expect to be able to form aggregates with solubilisates of different polarity in the different regions of core and shell, thereby opening the path to delivery systems that are able to carry both, unpolar and polar active agents at the same time. As we are working with PAA stabilized systems we will then study the pH response of these loaded IPEC micelles in the relevant pH range of 5-8. The focus will be on structural changes occurring as well as on the release kinetics for different active agents (payload) contained. The release will in general depend on structure and molecular composition of the IPEC micelles, as well as on pH, which means it can be triggered by a pH-change. This will mainly be studied by fluorescence measurements (high sensitivity) and allows to determine how versatile the IPEC-micelles can be tuned for such release experiments. In general, the comprehensive characterisation of these complex colloids will yield a substantial advancement of the scientific understanding for using IPEC micelles for selective solubilisation and release, thereby bringing such systems closer to potential applications.