Liquid crystal ordering in the hexagonal phase of rod-coil diblock copolymers

Density functional theory of rod-coil diblock copolymers, developed recently by the authors, has been generalised and used to study the liquid crystal ordering and microphase separation effects in the hexagonal, lamellar and nematic phases. The translational order parameters of rod and coil monomers and the orientational order parameters of rod-like fragments of the copolymer chains have been determined numerically by direct minimization of the free energy. The phase diagram has been derived containing the isotropic, the lamellar and the hexagonal phases which is consistent with typical experimental data. The order parameter profiles as functions of temperature and the copolymer composition have also been determined in different anisotropic phases. Finally, the spatial distributions of the density of rigid rod fragments and of the corresponding orientational order parameter in the hexagonal phase have been calculated

Design, Synthesis, and Properties of Novel Bio-Based and Ethylene-Based Copolymers

Erneuerbare Rohstoffe haben das Potenzial Erdöl-basierte Monomere in kontrollierten radikalischen Polymerisationen (RDRP) zu ersetzen. Dies ist wichtig, um eine Vielzahl unterschiedlicher Anwendungen, wie z.B. Klebstoffe oder Beschichtungen, nachhaltig bereit zu stellen. Es bestehen jedoch weiterhin Herausforderungen bei der Polymerisation von nicht-aktivierten und internen Doppelbindungen, wie sie häufig in natürlichen Molekülen vorhanden sind. Darüber hinaus fehlen nachhaltige Funktionalisierungsstrategien die Doppelbindungen an natürlich vorkommende Moleküle anbringen. Diese Dissertation setzt sich zum Ziel, eine Reihe erneuerbarer Monomere mittels kontrollierte radikalische Polymerisation für die Synthese von erneuerbaren und funktionellen (Co)Polymeren zugänglich zu machen. Die Polymerisationen wurden gezielt mit einem Kobaltkomplex (OMRP) durchgeführt, da diese die Polymerisation von einer Vielzahl nicht-akitivierter Monomere ermöglicht mit exzellenter Kontrolle über das Kettenwachstum unter milden Reaktionsbedingungen. Die jeweiligen Monomere wurden zunächst durch katalytische Reaktionen aus Pflanzenölen und/oder CO2 hergestellt und enthalten Ester oder Carbonat Gruppen, welche sich besonders für Post-Polymerisationsmodifikationen eignen. Die erfolgreiche kontrollierte radikalische Co-Polymerisation von diesen Monomeren, die nicht-aktivierte Doppelbindungen tragen, mit Vinylacetat und Ethen wurde bei milden Reaktionsbedingungen mit Hilfe eines Kobaltkomplexes (OMRP) durchgeführt. Die Polymerzusammensetzung konnte dabei durch die anfängliche Monomerzusammensetzung oder durch den Druck während der Polymerisation präzise kontrolliert und eingestellt werden. Die Einführung der Carbonatgruppen in Vinylacetat Co-Polymere erlaubte die Synthese von drei unterschiedlichen funktionellen Poly(Vinyl Alkohol) Co-Polymeren. Zudem wurde die kontrolliert radikalische Co-Polymerisation dieser funktionellen Monomere mit Ethen zum ersten Mal durchgeführt. Lineare Ethylen Co-Polymere mit einstellbarem Carbonatgehalt und daher wesentlich veränderten Eigenschaften im Vergleich zu Homopolyethylen konnten erhalten werden. Insbesondere erlaubt die genaue Abstimmung der molekularen Polymerparameter, wie molare Masse und Co-Polymerarchitektur, eine systematische Erforschung der Auswirkungen dieser Parameter auf die Fähigkeit des Co-Polymers als Phasenvermittlungs-Agent zu fungieren. Das Potenzial von Polyethylen Co-Polymeren mit funktionellen Gruppen als Seitenketten als Phasenvermittler wurde für Ethylen/Vinylacetat Co-Polymere veranschaulicht. Zuletzt wurde ein ausschließlich aus nachwachsenden Rohstoffen aufgebautes Polymer, basierend auf Stärke und Sonnenblumenöl mit hohem Ölsäureanteil, als Phasenvermittler zwischen Cellulose und stark verzweigtem Polyethylen (LDPE) eingesetzt. Eine verbesserte Dispersion der Cellulose in der LDPE-Matrix wurde rheologisch nachgewiesen, wobei sich die mechanischen Eigenschaften, insbesondere das Elastizitätsmodul, verbesserten. Diese Arbeit möchte somit auch auf die bislang kaum beschriebenen Vorzüge erneuerbarer Rohstoffe in der Synthese von funktionellen Polymeren für Anwendungen in Verbundwerkstoffen aufmerksam machen

Synthesis and Characterization of Cyclic Polypeptoids by Organo-Mediated Controlled Zwitterionic Ring-Opening Polymerization and Development of Redox-Responsive Polypeptoid Micelles as Drug Delivery Carriers

Peptoids are peptidomimetic polymers, which have attracted much attention over the past two decades. They have similar building blocks to peptides, and the similarity makes the backbone of peptoids hydrophilic and biocompatible.1 Two types of peptoid polymers are under development. One is sequence-defined peptoids, which exhibit excellent bioactivities.2 Another one is polypeptoids. The good biocompatibility and highly tunable side chain substituents allow polypeptoids to be used broadly in future biomedical applications. Varying polymer architectures, including linear polymers, cyclic polymers, comb-like polymers, and dendrimers can provide distinctive properties to the polymers. Cyclic polymers employ a cyclic architecture and lack chain ends, so their diffusion behaviors, aggregation behaviors, thermal transition behaviors, and crystallization behaviors are very different from the linear analogs. Facile synthetic approaches are required to expand the application of cyclic polymers into a broader scope. In chapter 1, the history of polypeptoids, the synthesis of cyclic polymers, the development of functional polypeptoids, and the cutting-edge biomedical research of polypeptoids were reviewed. In chapter 2, we reported our most recent work of the polymerization reaction of cyclic polypeptoids using a bicyclic amidine initiator. The study was described from the aspects of molecular weight control, identification of the polymerization, kinetics of the polymerization, and polymer architecture. Zwitterionic ring-opening polymerization of N-substituted N-carboxyanhydrides (R-NCA) mediated by the bicyclic amidine has been developed and well-defined cyclic polypeptoids can be synthesized. Pursuit of varying polymer architectures never ends because unique properties can be possibly discovered with the latest developed architecture. Besides cyclic polymers, linear bottlebrush polymers also attracted much attention due to their distinctive features. In chapter 3, we took one step forward and synthesized the cyclic bottlebrush polypeptoids. We then conducted a systematic study on the characterization of the cyclic bottlebrush polypeptoids and on the solution aggregation behaviors of zwitterionic cyclic polypeptoids with and without long side chains. It was revealed that zwitterionic cyclic polypeptoids tend to form clusters due to dipole-dipole interaction in methanol and even the long side chains cannot prevent this process. Another important direction of polypeptoid research, the biomedical application, was assessed in chapter 4. Redox-responsive micelles based on amphiphilic diblock copolypeptoids were prepared, and the solution stability, the morphology in dry state, the redox-responsive behaviors, drug release in vitro, and cell viability and cell inhibition activity of the micelles were completely studied

Different mechanisms of translational symmetry breaking in liquid-crystal coil-rod-coil triblock copolymers

A molecular-statistical theory of coil-rod–coil triblock copolymers with orientationally ordered rod-like fragments has been developed using the density functional approach. An explicit expression for the free energy has been obtained in terms of the direct correlation functions of the reference disordered phase, the Flory–Huggins parameter and the potential of anisotropic interaction between rigid rods. The theory has been used to derive several phase diagrams and to calculate numerically orientational and translational order parameter profiles for different polymer architecture as a function of the Flory–Huggins parameter, which specifies the short-range repulsion and as functions of temperature. In triblock copolymers, the nematic–lamellar transition is accompanied by the translational symmetry breaking, which can be caused by two different microscopic mechanisms. The first mechanism resembles a low dimensional crystallization and is typical for conventional smectic liquid crystals. The second mechanism is related to the repulsion between rod and coil segments and is typical for block copolymers. Both mechanisms are analyzed in detail as well as the effects of temperature, coil fraction and the triblock asymmetry on the transition into the lamellar phase

Polymeric hairy nanoparticles with helical hairs: synthesis and self-assembly, 2018

Nanoscale particles based on the nature of building blocks often self-assemble into superstructures with distinctive spatial arrangements which can be used as functional materials for different application. Micro-phase separated hairy nanoparticle with helical hair can self-assemble to form supramolecular material which may mimic the properties and functions of the natural polymers such as protein and cellulose. Beside this hairy/core-shell nanoparticles also may find many applications such as in asymmetric catalysis, nano-fillers in tire and rubbers, model systems for biology, lithography and as sensors. In this work, we have successfully synthesized two hairy nanoparticles both of which has cross-linked polystyrene core with helical poly (3- methyl 4- vinyl pyridine) and poly (2- methoxystyrene) brushes respectively by living anionic polymerization via one-pot synthesis. NMR spectroscopy was used to determine that polymerization was successful and compositions of HNPs have the agreement with the targeted HNPs structure. By tailoring the architecture (functionalization of polymer chains, the degree of polymerization, grafting density) of HNPs, it is possible to control the final properties of the system. Differential Scanning Calorimetry was used to demonstrate the thermal properties of the synthesized HNPs which corresponds to polymer composition. Dynamic light scattering, SEM and AFM images were recorded to measure the particle size and morphology of the particles. Circular dichroism spectroscopy was used to determine the induced chirality of helical polymer brushes by complexing it with the small chiral molecule. SEM and AFM imaging were recorded to find out the morphology and hierarchically self-assembly of the hairy nanoparticle system. The synthesized particles may have great potential to successfully generate self-assembled suprastructures which can further solve the chiral resolution problem and can also find different applications. KEY TERMS: Hairy Nanoparticles, Self-assembly, Chiral Polymer, Nanostructure, Poly(3-methyl-4-vinylpyridine), Poly (2-methoxystyrene), Chemistry, Materials Chemistry, Organic Chemistry, Polymer Chemistr

Understanding the effects of multivalent glycopolymer structure on molecular recognition

Carbohydrate-protein interactions are involved in a large number of important physiological and pathological processes. The weak binding affinity of a monovalent carbohydrate is compensated by multivalency in which multimeric recognition elements interact with a cell surface display of two or more receptors. In order to study lectin-carbohydrate interactions and find analytical and diagnostic applications, a large number of synthetic glycoconjugates have been investigated in the last decade. In order to explore the effects of structural features of glycopolymers on the binding events, a series of polymers were synthesized. Multivalent ligands with pendant saccharide moieties were prepared from two different types of backbones via ruthenium catalyzed ring-opening metathesis polymerization (ROMP). Several functional groups and neutral and charged spacers were introduced onto the backbone to explore binding of glycopolymers to cholera toxin B subunit (CT B5) The interactions of cholera toxin and the polymers were determined using the intrinsic fluorescence of the Trp 88 residue in the cholera toxin binding site. As sugar epitopes in polymers bind to CT B5, a variable decrease in fluorescence was observed. The improvement in inhibition over glycopolymers was also observed using competitive ELISA experiments. The interesting insight we found was that self-assembly of glycopolymers was involved in lectin binding events. Since glycopolymers have hydrophobic backbone and hydrophilic sugar moieties, glycopolymers form micelles and aggregates which derive from hydrophobic interactions of polymer backbone and inter- or/and intra-molecular hydrogen bonding of sugars. Further studies to identify polymer behaviors in aqueous solution were carried out by measuring their critical micelle concentration (CMC) and determining their size and morphology by dynamic light scattering (DLS) and transmission electron microscopy (TEM). These studies revealed that norbornene-based and cyclobutene-based polymers containing sugar moieties self-assemble into micelles and vesicles. The polymer particles were spherical and their size was heterogeneous. Binding of the cholera toxin B5 protein did not induce further aggregation. In glycopolymer particles, hydrophilic sugar moieties are located on the surface and hydrophobic backbones which composed of backbones of polymers are inside. In the recognition of lectin by synthetic glycopolymers, the binding affinity of glycopolymer was significantly inversely correlated with the self-assembled polymeric structure. | 155 page

Configurational properties of polyphenylene precursor polymers

The configurationally changes of a soluble precursor polymer. poly(5,6- dlmethylcarboxycyclohexadi-l.S-ene) have been studied during it’s conversion to poly(phenylene) by thermal aromatisation. This was performed principally in solution in N-methylpyirolidinone and chloroform, by size exclusion chromatography, viscometry and scattering techniques. The results show the polymer is initially a random coil, and during aromatisation stiffens to a wormlike chain, the intermediate to the rodlike molecule. This is evidenced by increased persistence length and increased dependency of size on molecular weight. The conversion to a stiffer molecule is accompanied by chain scission, more pronounced for high molecular weight polymers, and agglomeration, with consequential increased polydispersity and scatter in results. At 30% aromatisation aggregates dominate the behaviour of the solution, and at 40% the polymer becomes insoluble. Results from each technique differ according to the relative sensitivity to the two species present Aggregates exist as low as 10% aromatisation, suggesting the formation of contiguous phenylene nuclei, dispersed phenylene would not cause aggregation. When separated from the solution the aggregated species was found to be only slightly more aromatised than the free chain equivalent, and chemically very similar, suggesting aggregation arises from the arrangement rather than the quantity of phenylene monomers. The scattering behaviour of lightly aromatised polymer conformed to a wormlike chain model, while the aggregated polymer's scattering is close to that of a star model, suggesting a fringed micelle structure with a core of closely packed phenylene blocks, and arms preferentially composed of precursor polymer, with randomly dispersed phenylene. The insolubility of partially aromatised poly(DHCD-DMC) is common to other studies of polymers with conjugated backbones in which change from a good to a poor solvent causes a change from random coil to aggregated stiff chains

Anionic biopolymer derivatives and their performance in flocculation

The aim of the thesis is to identify and test anionic biopolymer derivatives in flocculation application. Several potential polysaccharides are listed in literature, but chemical modification is often needed to improve their performance in the selected application. Totally 28 polysaccharide derivatives were received from varying suppliers and screened by rheology and charge. The most potential biobased products in addition to synthetic polyacrylamide references were purified by dialysis and characterized by charge density, apparent viscosity in water and brine and intrinsic viscosity in brine. Xanthan gum, carboxymethyl cellulose and guar gum appeared to have the best combination of high viscosity and charge density. Xanthan gum revealed exceptional behavior in brine as its viscosity increases upon salt addition due to helix formation. This phenomenon opens numerous possibilities in brine applications. In the application testing 9 biopolymer derivatives representing 6 different types of polysaccharides in addition to two reference polyacrylamides were studied by flocculating bentonite. The evolution of flocs was monitored online with focused beam reflectance measurement. Xanthan gum, carboxymethyl cellulose and guar gum have the best performance in flocculation as expected based on the characterization results supporting the statement that size and charge are key parameters in flocculation performance. The biobased products fall behind in flocculation efficiency compared to polyacrylamides, but their performance can be improved by chemical modification. A quick thermal stability screening was also performed, and xanthan gum appeared to be even more thermally stable compared to the polyacrylamide reference in the selected environment. As a conclusion it is justified to claim that in the future the biobased products have a great potential to offer alternative solutions in the applications where synthetic fossil-based polymers are currently used. The recommended path forward is to find suitable modification mechanisms to increase the flocculation performance of xanthan gum, carboxymethyl cellulose and guar gum. Nucleophilic reaction of the saccharide oxygen is a typical example of chain modification for polysaccharide chemistry. Based on the results presented in this thesis, the future of biobased products from renewable resources looks promising