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

本课题研究了密集接枝共聚物（分子刷，MB）在溶液和凝胶状态下的行为。MB侧链是双嵌段或无规共聚物的热响应和永久亲水段。改变分子参数，如主链长度、侧链片段的长度和序列，可以产生丰富的相和自组装行为。作为一个体系，我们选择聚（2-恶唑啉）s，因为可以通过选择2-取代来微调片段的水溶性。MB的主链将由聚（2-异丙基-2-恶唑啉）和（水溶性）聚（2-甲基-2-恶唑啉）和（热响应性）聚（2-异/n-丙基-2-恶唑啉）的侧链组成。从具有短骨架到长骨架的POx开始，mb的形状将从球形到拉长不等。MBs的相行为将通过系统地添加热响应片段和两亲基序（远端和核心块或随机）来调整。因此，现有的合成方法必须进一步发展，使用活阴离子和可控自由基聚合技术。此外，我们将开发更复杂的聚合物结构（星形mb和哑铃），目的是通过单分子纳米物体的亲水和疏水体素来形成复杂的凝胶和程序化的自组装行为。MBs的温度依赖性行为将在稀水溶液和浓水溶液中根据分子结构进行研究。重点研究了热响应块体的坍塌对其尺寸和形状、内部结构、自组装、凝胶形成和开关行为以及集体动力学的影响。为此，采用了荧光相关光谱、动态光散射、小角x射线和中子散射等方法。这些实验研究将伴随着俄罗斯合作伙伴的计算机模拟，他们将重点关注MBs在选择性溶剂中的自组装，单分子到多分子团簇/胶束的形成以及自组装物理水凝胶的膨胀/崩溃行为。模拟方法包括开发合成共聚物及其介观粗粒度类似物的原子模型，这些模型将通过耗散粒子动力学或分子动力学进行研究。先进的聚合物合成、实验结构研究和计算机模拟的独特结合将使人们全面了解具有复杂结构的热响应分子刷的行为。

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.