Supramolecular assembly of functionalized polymers: straightforward synthesis and dynamic investigations of individual nanostructures

Understanding self-assembly of matter on the nanometer scale is crucial in modern materials’ science to increase the control over novel properties such as responsiveness and reversibility for, e.g., self-healing or stimuli-repsonive materials. The results shown in this thesis discuss the use of difunctional initiators in nitroxide-mediated polymerization for the one-step preparation of telechelic polymers with supramolecular bondings sites – namely 2-ureido-4[1H]-pyrimidinone as hydrogen bonding and 2,2’:6’,2‘’-terpyridine as metal complexing moieties – and its use for defined self-assembly towards responsive and amphiphilic linear suprapolymers. The approach is suitable to easily adjust the polymeric spacer between the supramolecular binding sites to optimize features such as reversibility for efficient responsive architectures. Since supramolecular assembly is also driven by self-assembly of covalently bonded block copolymer segments, ABC triblock oxazolines containing fluorophilic block were investigated by cryoTEM investigations showing unique examples of the coexistence of lamellar and bicontinuous phases in transient structures in solution. However, hierarchical or dynamic processes of these supramolecular assemblies can not be characterized by the static nature of cryoTEM. The introduction of ionic liquids as liquid media in TEM enables for the first time with low preparative efforts the possibility to investigate dynamic processes of individual supramolecular assemblies on the nanometer scale. For example, the motion of block copolymer assemblies were investigated in-situ revealing individual motion of the particles in the free-standing ionic liquid films. Also dynamic processes of assemblies of block copolymer containing insoluble blocks with low glass transition temperatures were observed in situ showing deformations, e.g. membrane fission of vesicles, upon beam irradiation

Revealing the Deposition Mechanism of the Powder Aerosol Deposition Method Using Ceramic Oxide Core–Shell Particles

The powder aerosol deposition (PAD) method is a process to manufacture ceramic films completely at room temperature. Since the first reports by Akedo in the late 1990s, much research has been conducted to reveal the exact mechanism of the deposition process. However, it is still not fully understood. This work tackles this challenge using core–shell particles. Two coated oxides, Al2O3 core with a SiO2 shell and LiNi0.6Mn0.2Co0.2O2 core with a LiNbO3 shell, are investigated. Initially, the element ratios Al:Si and Ni:Nb of the powder are determined by energy-dispersive X-ray spectroscopy (EDX). In a second step, the change in the element ratios of Al:Si and Ni:Nb after deposition is investigated. The element ratios from powder to film strongly shift toward the shell elements, indicating that the particles fracture and only the outer parts of the particles are deposited. In the last step, this work investigates cross-sections of the deposited films with scanning transmission electron microscopy (STEM combined with EDX and an energy-selective back-scattered electron (EsB) detector to unveil the element distribution within the film itself. Therefore, the following overall picture emerges: particles impact on the substrate or on previously deposited particle, fracture, and only a small part of the impacting particles that originate from the outer part of the impacting particle gets deposited

Clickable initiators, monomers and polymers in controlled radical polymerizations – a prospective combination in polymer science

Preparation of multifunctional and well-defined macromolecules requires a smart selection of the most suitable controlled polymerization technique in combination with appropriate click reactions. In this review, we provide an overview on the use of various ‘‘clickable’’ initiators and monomers as well as on the postpolymerization modifications that have been widely used to construct clickable macromolecules. As such, this contribution will aid polymer chemists to select a suitable combination of CRP and click methodologies to design the target structures

Orthogonal self-assembly of stimuli-responsive supramolecular polymers using one-step prepared heterotelechelic building blocks

The one-step preparation of heterodifunctional telechelic polymers containing 2,2':6',2 ''-terpyridine (tpy) and 2-ureido-4[1H]-pyrimidinone (UPy) end-groups, as orthogonal supramolecular moieties, is reported. The utilization of an appropriately functionalized alkoxyamine, as an initiator for the nitroxide-mediated radical polymerization (NMP), directly constitutes the end-groups of the resultant polymers. The targeted alkoxyamines are based on the nitroxide structure of 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane (TIPNO) and were obtained via stepwise functionalization of a heterodifunctional alkoxyamine skeleton. Controlled radical polymerization of styrenics using the alkoxyamine tpy-TIPNO-UPy, as an initiator, is demonstrated to generate well-defined telechelic polymers in one step. These telechelics represent promising building blocks for supramolecular architectures via self-assembly processes, yielding linear chain-extended polymers of high molar masses. Due to the orthogonality of the metal ion complexation and hydrogen bonding, the system can be addressed selectively by external stimuli. Besides for various applications, e.g. as self-healing materials, the strategy is highly attractive for tailoring the material's properties of supramolecular polymers, since the nature and the length of the polymer chain between the terminal supramolecular motifs can be controlled in a facile way

Tuning the morphology of triblock terpoly(2-oxazoline)s containing a 2-phenyl-2-oxazoline block with varying fluorine content

The formation of nanostructures in triblock terpolymers consisting of poly[2-ethyl-2-oxazoline-block-2-(1-ethylpentyl)-2-oxazoline-block-2-(Xfluorophenyl)-2-oxazoline] (X = di, tri, tetra and penta) was investigated in water. For this purpose a gradually increasing degree of fluorination was introduced in the molecular structures and its influence on the self-assembly was studied. It can be demonstrated that the basic form of aggregation of these systems resembles rod-like micelles, which tend, upon introduction of fluorinated blocks, to aggregate first into 2-dimensional and later into 3-dimensional super-aggregates. In the case of di- and pentafluorinated terpolymers well-defined structures were observed, which represent likely intermediate, stable transient structures formed during an assumed rod-to-vesicle transition. DLS and cryo-TEM were utilized to analyze the structural features of these nanostructures and a model for their further assembly into super-structures was developed