Effect of Solvent Quality on the Solution Properties of Assemblies of Partially Fluorinated Amphiphilic Diblock Copolymers

The effect of solvent on the formation of assemblies of partially fluorinated block copolymers in solution has been examined. Two classes of materials based respectively on 2,2,2-trifluoroethyl acrylate (TFEA) and 2,2,2-trifluoroethyl methacrylate (TFEMA) were dissolved in organic solvents, and the properties on successive addition of water were studied using NMR spectroscopy, NMR imaging, AFM, and TEM. The relatively high glass transition temperature of the methacrylate blocks resulted in the formation of kinetically trapped structures that could only be resolved following heating to temperatures well above the T_g. The acrylate polymers formed loose assemblies in pure dimethylformamide, and on addition of water cylindrical micelles were observed. On the other hand, in pure acetone the partially fluorinated segments interacted more strongly with the solvent, with this structure inverting on addition of water. The NMR parameters were strongly dependent on the proposed structures in solution, and most markedly the mutual association of the fluorinated segments resulted in strong dipole–dipole interactions with the ¹⁹F spins. The importance of structure and solvent on the potential of these copolymers as MRI contrast agents is discussed, and broad design rules for effective ¹⁹F MRI agents are given.