Authors:	Suraeva, Oksana
Title:	Polymer 2D crystals via crystallization self-assembly: preparation, properties and features
Online publication date:	30-Mar-2022
Year of first publication:	2022
Language:	english
Abstract:	Polymer 2D structures are a wide class of materials with unique properties, coming from their highly anisotropic nature. Functional 2D polymers may prove useful as membranes, chemical platforms for catalysis, optoelectronic devices, ultrasensitive pressure sensors and in environmental science. This thesis focuses on the formation of polymer 2D crystals, comprising the synthesis of polymers with incorporated functional groups, crystallization driven formation of 2D crystals and subsequent functionalization of the functional groups on the crystal surface. Several parameters determine this process. From the synthesis part, the introduced functional groups should be equidistantly distributed along the polymer backbone to facilitate controlled crystallization and to yield a perfect arrangement of the functional groups on the crystal surface. This was achieved by using acyclic diene metathesis (ADMET) polymerization. During crystallization, introduced functional groups will be expelled from the crystal lattice forming a functional surface. By varying the length of aliphatic part between the groups, we can change thermomechanical properties of the obtained crystals. From the crystallization part, parameters such as choice of solvent, concentration of polymer, temperature and speed of crystallization define the size and shape of the final crystals. By varying these parameters, we adjust the optimal condition to form polymer 2D nanocrystals with the desired thermomechanical properties. Moreover, a sequential polymer solution crystallization (SPSC) approach allows to achieve a laterally structured chemical functionalization on the surface of polymer nanoplatelets - where the core and the rim of the crystal surface have a different functionality. Variable functional groups thus can be placed on the surface, whereby the obtained nanocrystals have a broad potential application. Chapter 1 describes crystallizable polymers as part of colloidal chemistry and the importance of 2D polymer crystals for the various applications. It is demonstrated which mechanisms are responsible for the crystallization process in solution and in bulk and how seeded growth approach helps to form uniform polymer crystals. In this chapter, we show that shape and properties of obtained 2D platelets depends on many parameters, such as size and functionality of incorporated groups, frequency and regularity of their distribution, speed and temperature control of the crystallization process. As a result, we can use crystallizable polymers as a uniform platform to obtain 2D nanoplatelets with programmable physical and chemical properties. Depending on the requirements for the final composition, one can choose among three distinct groups of initial materials: synthetic homogeneous homopolymers, block copolymers and bio-based polymers. Taken together, this chapter is intended as a contribution towards evaluating the potential of crystallizable polymers as a promising way to obtain 2D nanomaterials. Chapter 2 presents an impact of the frequency of incorporated defects on the structure and properties of obtained polymer 2D nanoplatelets. The solution-crystallized anisotropic polymer platelets are based on PE-like polyphosphates with a variable length of methylene spacers (20, 30, and 40 CH2 groups between each phosphate group). Linear polyphosphates with molecular weights up 23,100 g mol-1 were prepared by acyclic diene metathesis (ADMET) polymerization. Post-polymerization hydrogenation yielded solid, PE-like materials. Crystallization of these polymers into 2D polymer platelets was achieved by crystallization from dilute solution. The morphology of the polymer crystals was investigated using differential scanning calorimetry (DSC), small-angle X-ray diffraction (SAXS), wide-angle X-ray diffraction (WAXD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). With extending the length of aliphatic segment, melting points increases from 56 to 62 and 91 °C. The thickness of crystalline part, as well as the total thickness of crystals lamellar, increased from the sample with 20 CH2 to 40 CH2. At the same time, by changing the length of aliphatic spacer from C20 to C40 a change in crystal structure from pseudo-hexagonal to orthorhombic was observed. These findings demonstrate that the functional groups in the PE chain act as defects for the crystallization process. With increasing defect concentration, the crystal lattice becomes distorted. Moreover, the direct correlation of the crystal thickness with the length of the aliphatic segment clearly demonstrates that the in-chain functional groups are expelled to the lateral surface of the 2D nanoplatelets. Chapter 3 presents the formation PE-derivatives with equidistant in-chain thiophene groups, capable of further postfunctionalization. Two polymers with 20 and 38 CH2 groups between thiophenes were synthesized to show the effect of the variation of the length of aliphatic part on the properties of the resulting polymer crystals. Thiophene was integrate in the polymer chain to introduce conductive properties to the obtained polymer crystals. Polymers were prepared by acyclic diene metathesis (ADMET) polymerization. Thermomechanical properties of the synthesized polymers were characterized using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). Because the polymer with the 20 CH2 spacer does not reveals crystalline structure at the room temperature, all postfunctionalization experiments were conducted with 38 CH2 polymer. During crystallization, the thiophene groups are expelled to the crystal surface. Subsequently, they were copolymerized with 3,4-Ethylenedioxythiophene (EDOT) molecules, forming conductive 2D platelets. Chapter 4 focuses on the influence of the incorporated chemical groups on the properties of obtained material. Here, we perform the synthesis and characterization of polyethylene-based polymers containing vitamin C groups in the polymer chain. Polymers with molecular weights up to 35,800 g mol-1 were prepared by acyclic diene metathesis (ADMET) polymerization. Post-polymerization hydrogenation leads to formation of a fully saturated, semicrystalline polymer with a precise spacing of 20 CH2 groups between vitamin C groups. During crystallization, the vitamin C groups are expelled from the crystal and are located on the basal surface of the crystals. Thermomechanical properties and morphology of the polymer crystals were investigated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray diffraction (SAXD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Furthermore, incorporation of vitamin C groups in the polymer backbone introduces bioactive properties, such as radical scavenging. Moreover, the polymer is not cytotoxic and is taken up by cells, which makes it a suitable candidate for biomedical applications. Chapter 5 is dedicated to the problem that two-dimensional nanoplatelets commonly have a homogeneous surface. Therefore, structuring the surface of a nanoplatelet is a major challenge. By consecutively crystallizing polymers with a precise molecular architecture and different functional groups in the polymer backbone, we can form 2D organic nanoplatelets with a heterogeneously functionalized surface. We achieve this by using polymers with the same length of aliphatic part in a two-step approach: crystallization of first polymer to form a core followed by cocrystallization of second polymer around it. As a result, the central area of the platelets has a different surface functionality than the periphery. Obtained platelets are stable in dispersion, which considerably simplifies their further chemical modification and processing. Furthermore, various functional groups can be incorporated into the backbone of the initial polymers, what makes this simple concept a promising platform to create a new class of nanostructured 2D materials with desirable and controllable surface functionality. In Chapter 6 we considered functionalized polymer 2D platelets, obtained from solution crystallization, as synthetic secondary structures and investigated their supramolecular interactions and ability to fold. It is known, that in nature complex biomolecules fold into defined structures by various intra- and intermolecular interactions. Primary structures, consisting of a linear sequence of nucleotides or amino acids, self-assemble to secondary alpha helices and beta sheets structure or protein tertiary structures. In synthetic polymers, single chain nanoparticles have been used as simple mimics of macromolecular chain folding. However, folding of polymer platelets had not been achieved so far. To achieve this, we functionalized a PE-like polyphosphate with pendant terpyridine groups. This polymer was crystallized from solution to form a functional polymer platelet dispersions, i.e. the synthetic secondary structure. By the addition of nickel salts to the dispersion, the strong metal-terpyridine complexation lead to a folding of the polymer platelets into a “synthetic tertiary structure”, which was investigated by TEM. Hereby, the size of the obtained assemblies could be altered by varying the concentration of metal ions present. Such assemblies might be used in catalysis or for the generation of hierarchical assemblies.
DDC:	540 Chemie 540 Chemistry and allied sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-5525
URN:	urn:nbn:de:hebis:77-openscience-ff941725-f337-40d2-97bc-b8009144b3011
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	http://rightsstatements.org/vocab/InC/1.0/
Extent:	146 Seiten, Illustrationen, Diagramme
Appears in collections:	JGU-Publikationen