Molecular brushes with amphiphilic thermoresponsive side chains – from synthesis over solutions to self-assembled gels

点击翻译按钮获取中文摘要

The research project addresses the behavior of dense graft-copolymers (molecular brushes, MB) in solution and gel state. The MB side chains are diblock or random copolymers of thermoresponsive and permanently hydrophilic segments. Varying the molecular parameters, such as the backbone length, the lengths and sequence of the segments in the side chains results in rich phase and self-assembly behavior. As a system, we chose poly(2-oxazoline)s because the water solubility of the segments can be minutely fine-tuned by the choice of the 2-substitution. The backbone of the MB will consist of poly(2-isopropenyl-2-oxazoline) and the side chains from (water-soluble) poly(2-methyl-2-oxazoline) and (thermoresponsive) poly(2-iso/n-propyl-2-oxazoline) segments. Starting from POx MBs with short to long backbones, the shape of the MBs will be varied from spherical to elongated. The phase behavior of the MBs will be tuned by the systematic addition of thermoresponsive segments and the amphiphilic motif (distal and core blocks or random). Therefor, the established synthesis has to be further developed, using living-anionic and controlled radical polymerization techniques. Additionally, we will develop more complex polymer architectures (star-like MBs and dumb-bells) with the aim of complex gel formation and programmed self-assembly behavior by hydrophilic and hydrophobic voxels of the single-molecule nanoobjects. The temperature-dependent behavior of the MBs will be studied in dilute and concentrated aqueous solutions in dependence on the molecular architecture. The focus is on the influence of the collapse of the thermoresponsive blocks on the size and shape, the inner structure, the self-assembly, gel formation and switching behavior and the collective dynamics. At this, the methods fluorescence correlation spectroscopy, dynamic light scattering and small-angle X-ray and neutron scattering. These experimental investigations will be accompanied by computer simulations by the Russian partner, who focuses on the self-assembly of the MBs in selective solvents, the formation of uni- to multimolecular clusters/micelles and the swelling/collapse behavior of self-assembled physical hydrogels. Simulation methods include the development of atomistic models of synthesized copolymers and their mesoscopic coarse-grained analogues, which will be studied via either dissipative particle dynamics or molecular dynamics. The unique combination of advanced polymer synthesis, experimental structural investigations and computer simulations will give comprehensive insight into the behavior of thermoresponsive molecular brushes with complex architecture.