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Preparation and Supramolecular Structure Investigations of Ionic Interaction Based Polyelectrolyte-Dendron Complexes

Author: ZhangXinJun
Tutor: WangWei
School: Nankai University
Course: Polymer Chemistry and Physics
Keywords: Polyelectrolyte Branches tablets Complexes Supramolecular Self-assembly
CLC: O631.1
Type: PhD thesis
Year: 2009
Downloads: 155
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Abstract


Dendronized polymer is a type of side chain branches piece new tree polymer, and in recent years has attracted more and more interest in the study, their special molecular structure and its inherent nature are inseparable. Dendron primitives steric effect, by controlling the structure of dendrons primitives, the distance between the kind or algebra, graft ratio, and the main polymer chain, in order to achieve the configuration of the type of polymer chain, The flexibility and control of the molecular size. As the of primitives size of the branches connected to the main polymer chain (algebraic) increases, the conformation of the corresponding polymer can be converted from a random coil semi-rigid or rigid cylinder. Therefore, this type of large-size, high rigid polymer chain configuration flexibility will help to conduct in-depth understanding of polymer chemistry and physics disciplines, and the formation of columnar nano molecular surface or internal functional groups modified and modified, will be a very meaningful work. Scientific community, the research has made encouraging progress, dendronized polymer from the bottom (bottom-up) as a class of effective means of preparation of nano-molecular materials, I believe in the near future, will be in biomedicine optoelectronic functional materials have a huge space for development. Their synthesis so far is still more difficult, however, graft law and macromonomer method usually there are a lot of limitations, such as a large excess feeding, longer reaction cycle, complex purification steps and even some separation basic is not feasible, and the yields are often not high. Therefore, looking for a relatively easy way to synthesize such polymers have important practical significance. Supramolecular chemistry, research of two or more chemical species having a specific structure and function of supramolecular systems scientific conclusion made by non-covalent bond with intermolecular forces, these forces including the role of ionic bond, hydrogen bond, a hydrophilic hydrophobic interaction, dipole-dipole interaction, van der Waals forces, π-π stacking interactions and coordination role. Which the main driving force for the ion key role in the self-assembly behavior called ion self-assembly, the advantages of simple synthesis, structural perfection and stability, strict 1:1 charge stoichiometry of the resulting supramolecular structure. Polyelectrolyte - surfactant complex is the perfect application of ion self-assembly, Production and Purification of simple, easy functionalization, and can form highly ordered supramolecular structures caused widespread concern. However, due to the relatively simple using the surfactant structure, the formation of the ordered structure of the thus prepared composite in the solid state is generally lamellar phase, and its poor solubility in a certain extent, limit their solution behavior research. So far, only a very small amount of work the complex structure of the side chain to introduce this system, the understanding of the people in this area is still in its infancy. In this article, we will combine dendronized polymers and polyelectrolytes - Surfactant complexes two concepts proposed by uncharged dendrimers amphiphilic molecules with a polyelectrolyte of opposite charge by the action of ionic bond composite Preparation of the strategy of the branches of polymer. Three branches sheet potassium salt can be ionomer composite effect occurs with a polyelectrolyte in an aqueous solution, and the product precipitated to precipitate the form, the reprecipitation purification step by washing with water that is able to obtain high-purity object product, three generations of composite preparation process, respectively PG1, PG2 and PG3. Experimental work, mainly using nuclear magnetic resonance (to 1H-NMR), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-vis) and elemental analysis (EA) confirmed the molecular structure of the complex, confirmed this strategy through the chemical synthesis of supramolecular dendronized polymer practicable. Compared with conventional polymer based on covalently grafted branches synthesis, the preparation and purification methods used herein are very simple, and also higher yield, but also due to the introduction of the ionic bond and dendrimers sidechain, the composite was expected in the solution and in the solid state have different properties. Firstly, the complexes prepared using the polymer conformation in solution. In an organic in dilute solution, the static light scattering (SLS) with the collapse of the random coil conformation confirmed PG1, PG2 and PG3, showing the nature of the polyelectrolyte; measured three generations of dynamic light scattering (DLS) complexes have the same The hydrodynamic radius of the three polymer should have a similar random coil conformation. Also observed under an atomic force microscope (AFM) to the generation of the spherical aggregates, we believe that they are associated with the generation of the line group. Based on test results, we propose herein branches prepared polymer complex in the organic dilute solution using fancy (flowerlike) the conformation of the clew, i.e. the polymer chain to form a loop around the charge around the clusters. This conformational clusters in a dilute solution of the polymer plays a role of the intramolecular crosslinking agent, is substantially offset by the increased resistance caused by the bit of the polymer backbone extending trend. The clusters generated driving force and the charge remaining on the polymer main chain not repellent effect of solvent. This conformational traditional covalently grafted branches polymers are very different, can be used to explain the dendron formed of a polymer prepared by the action of ionic bond, the tacticity of the ordered structure of the supramolecular lower experimental facts. Further work, we study prepared dendronized polymer assembly behavior in solution. Since the introduction of the ionic bond, which is very sensitive to the ionic strength of the system, by self-assembly induced by the outer salt. Light scattering (LS) experiment together affirm this nature combined with electron microscopy (EM), we found that with the system increase in the salinity of composite will first gather to form a multilayer micelle, having a radius of about 40 nanometers; further increase the salt concentration causes the micelle to the radius of the transition of a thin layer of about 100 nm vesicles; subsequent further increase of salinity in the solution generating macro-visible precipitate, and along with the emergence of micron Giant Vesicles. We believe that this is the twigs sheet molecules polyelectrolyte having a strong assembling ability as the template for the self-assembly, it arises because the salt is added to suppress the entropic effects of the ions in solution, thus promoting the phase separation. Aggregate morphology of different, is caused due to the polarization of the different area of ??the ionic bond, the molecular shape of the polymer repeat unit different. Such environmental response of the polymer is an important property of these complexes. While in the solid state, thermogravimetry (TGA) and differential scanning calorimetry (DSC) experiments show the higher thermal stability of the prepared complexes, the benzene rings in the molecule of the cluster structure and twigs sheet plays a very stable complex important role. The wide-angle X-ray diffraction (WXRD) and small angle X-ray scattering (SAXS) confirmed that three generations of complex forming ordered supramolecular structures available in the solid state, PG1 layered structure can be observed under a polarizing microscope (POM) to its The formation of the liquid crystal texture. With algebra increase branches chip molecular volume increase, the second and third generation complex formation structure ordered deteriorate, LCD phenomenon is not observed in the POM, but SAXS PG2 experience from lamellar phase to columnar phase transition PG3 is typical hexagonal columnar stacking. Supramolecular structure changes from the non-polar branches sheet molecules increases with algebraic result of volume increase caused, fully consistent with the phase separation of the block copolymer of the classic theory. In the last chapter, we use twigs piece molecules synthesized two kinds of dendritic amphiphilic molecules with different molecular shape and more rigid. TEM and AFM joint showed that the two molecules are able to spontaneously formed in the selective solvent hexane trans unilamellar vesicles, but there are very significant differences in the size of the vesicle, the molecular geometry is considered to be caused by this difference. reasons. The energy change of the amphiphilic molecules in the formation of the bilayer membrane (bilayer), is determined by the bending energy, which leads to having a different radius of curvature of molecules forming aggregates of different sizes and even of different morphologies. This work shows that by changing the molecular shape to achieve the purpose of manipulating the morphology and size of the self-assembly and self-assembly (self-assembly), as well as guiding assembly (direct-assembly), which has an important theoretical and practical significance.

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CLC: > Mathematical sciences and chemical > Chemistry > Polymer chemistry ( polymer ) > Polymer physics and physical chemistry of polymers > Theory of polymer structure
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