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| Author | : 安家幸 |
| Publisher | : |
| Total Pages | : 88 |
| Release | : 2008 |
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| Author | : Xiaojun Wang |
| Publisher | : |
| Total Pages | : 250 |
| Release | : 2012 |
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This dissertation presents a review on state-of-the-art research of well-defined charged block copolymers, including synthesis, characterization, bulk morphology and self-assembly in aqueous solution of amphiphilic block polyelectrolytes. In Chapter 1, as a general introduction, experimental observations and theoretical calculations devoted towards understanding morphological behavior in charged block copolymer systems are reviewed along with some of the new emerging research directions. Further investigation of charged systems is urged in order to fully understand their morphological behavior and to directly target structures for the tremendous potential in technological applications. Following this background, in Chapters 2, 3, 4 and 5 are presented the design and synthesis of a series of well-defined block copolymers composed of charged and neutral block copolymers with full characterization: sulfonated polystyrene-b-fluorinated polyisoprene (sPS-b-fPI) and polystyrene-b-sulfonated poly(1,3-cyclohexadiene) (PS-b-sPCHD). Their bulk morphological behaviors in melts and self-assembly of sPS-b-fPI, PS-b-sPCHD in water were investigated. Some unique behaviors of sPS-b-fPI were discovered. The mechanisms for formation of novel nanostructures in aqueous solution are discussed in details in Chapter 4. Spherical and vesicular structures were formed from strong electrolyte block copolymers, e.g. PS-bsPCHD. Detailed light scattering and transmission electron microscopy were applied to characterize these structures. The abnormal formation of vesicles as well as microstructure effects on self-assembly is discussed in Chapter 5. In Chapter 6, we describe the successful synthesis of a well-defined acid-based block copolymers containing polyisoprene while maintaining the integrity of the functionality (double bonds) of polyisoprene. A general purification method is also presented in order to remove homo polyisoprene, polystyrene, and PS-b-PI in the di-, and tri-block copolymers. The self-assembly of PS-b-PI-b-PAA triblock terpolymers was studied in order to form multicompartmental structures in aqueous environments. In the last Chapter 7, detailed synthesis and characterization of a novel conjugate: poly(L-leucine) grafted hyaluronan (HA) (HA-g-PLeu) are presented. This work describes a new method to synthesize HA-g-PLeu via a "grafting onto" strategy. Due to the amphiphilic nature of this graft copolymers, a "local network" formed by self-assembly which was characterized by atomic force microscopy and light scattering. The secondary structure of the polypeptide was revealed by circular dichroism.
| Author | : Xinjun Yu |
| Publisher | : |
| Total Pages | : 121 |
| Release | : 2015 |
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This dissertation is mainly based on the works of synthesis and characterization of self-assembling polymers using hydrogen bonding or hydrophobic interactions. Firstly, N-alkyl urea peptoid oligomer was synthesized as backbone of supramolecular polymers through three step repetition cycles with high yield. One N-alkyl urea peptoid precursor was explored to simplify the synthetic process. 4 different functional groups were converted from one precursor. Then 2-ureido-4[1H]-pyrimidinone (UPy) group which is a quadruple hydrogen bonding system was incorporated to N-alkyl urea peptoid oligomers to generate supramolecules. With the experience of UPy unit, we further explored UPy containing monomer to make organogelators. Three different monomers with different Tg values were copolymerized using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Organogels were afforded in both chloroform and dichlorobenzene. Critical gelation concentration and mechanic properties of organogels were examined. Cooperating another novel monomer containing pyrene unit to the above copolymers, fluorescent organogels were achieved which were suitable for potential up-conversion applications. In addition to pyrene, anthracene is another molecule which shows great up-conversion property. A series of Poly[(9-anthrylmethyl methacrylate)-co-(methyl methacrylate)] (Poly(AnMMA-co-MMA)) with different AnMMA ratios were synthesized via RAFT polymerization, resulting in tunable inter-chromophore distances. These polymers can serve as emitters, with PtOEP as sensitizer, in triplet-triplet annihilation up-conversion (TTA-UC) systems. TTA-UC intensity of the Poly(AnMMA-co-MMA)/PtOEP mixtures displays interesting dependence on the AnMMA ratio in the polymer. Interactions between chromophores on the same polymer chain play the key role in affecting the TTA-UC intensity in these systems. It is critical to minimize intra-chain chromophore quenching in order to achieve high UC intensity. Hydrophobic effect was used to obtain a hybrid photosensitizer. By integrating amphiphilic block copolymer poly(N-isopropylacrylamide-b-styrene) (PNIPAAm-b-styrene) stabilized silver nanoparticles (Ag NPs) with hematoporphyrin (HP), HP was trapped by polystyrene block through hydrophobic effects. Hydrophilic block can increase the solubility of this photosensitizer in aqueous solution. This hybrid photosensitizer was demonstrated to enhance singlet oxygen production. Finally, a self-immolative polymer was made with a kinetically stable polymer backbone, whose chain end can respond to external stimulus by triggering a head-to-tail depolymerizaiton. Electrospining was used to fabricate nano-scale fibers which can be utilized in potential drug delivery system.
| Author | : Michael Duane Determan |
| Publisher | : |
| Total Pages | : 296 |
| Release | : 2006 |
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Water-soluble stimuli responsive block copolymers are a rapidly emerging class of materials with great potential in biomedical and technological applications. In this work a novel class of pentablock copolymers are synthesized via atom transfer radical polymerization techniques and their stimuli-responsive self-assembly properties are characterized. Aqueous solutions of these materials are observed to form micelles and hydrogels in response to changes in both temperature and pH. Cryogenic transmission electron microscopy (cryo-TEM) and small angle neutron and X-ray scattering (SANS and SAXS) techniques are used to investigate the nanoscale structures formed by these pentablock copolymers in solution. The gel structure and mechanical properties are investigated with SANS and rheological techniques. The multi-responsive properties of these materials are utilized to formulate a stimuli responsive drug delivery formulation that exhibits thermoreversible gelation and pH dependent release rate of model drugs.
| Author | : Victor Ho |
| Publisher | : |
| Total Pages | : 132 |
| Release | : 2014 |
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Conjugated polymers have been widely studied for their use in lightweight, flexible, and solution-processable electronic devices. However, the optimization of such polymer-based devices has been largely Edisonian in nature due to both a poor understanding of and an inability to control the complex hierarchical structure observed in semicrystalline polymers. In this thesis, we show that simple chemical modifications to commonly-studied conjugated polymers can have a large effect on the observed structure ranging from the unit cell to that on the order of device features. In particular, the self-assembly of block copolymers in which one of the components is optoelectronically-active is presented as a facile method to obtain nanostructured materials. For the work in this thesis, we will focus on poly(3-alkylthiophenes), a widely studied class of conjugated polymers due to their favorable optoelectronic properties, high solubility in organic solvents, and susceptibility to simple chemical modification. Although the synthesis of conjugated block copolymers has been presented in the past, complexities arising from crystallization of the conjugated moiety have dominated the observed solid state morphologies. Specifically, the crystallization of the semicrystalline block dictates the block copolymer microphase separation, a well-known phenomenon in the literature for non-conjugated semicrystalline block copolymers, which has resulted in solid state morphologies that do not differ significantly from that of the semiconducting homopolymer. To address this, we first show that the side chain chemistry controls the thermal transitions and optoelectronic properties in poly(3-alkylthiophenes). Such control over the crystallization kinetics provides an experimentally convenient approach to investigate the importance of the crystalline structure over a wide range of length scales on the optoelectronic properties. Furthermore, the ability to control the thermal transition temperatures can be used to directly manipulate, and thereby balance, the competition between the driving forces for crystallization and self-assembly. As evidence, the nanoscale structure is shown to be directly controlled via synthesis of block copolymers in which one block is the low melting temperature semiconducting polymer, poly(3-(2-ethylhexyl)thiophene). A wide range of morphologies with curved interfaces are observed which, in the past, have been precluded by the crystallization of poly(3-alkylthiophenes) with unbranched aliphatic side chains such as poly(3-hexylthiophene). Importantly, confinement of the conjugated polymer to nanoscale domains is not detrimental to the crystallinity or to charge transport over device-scale dimensions. Additionally, this approach is shown to be effective for a number of different chemistries providing a flexible methodology for obtaining periodic, semiconducting domains on the nanoscale. Together, these simple synthetic strategies can be used to tune the morphology of various length scales of thin film active layers and provide synthetic rules for design of novel semiconducting polymer systems.
| Author | : Landesstelle Jugendschutz |
| Publisher | : |
| Total Pages | : 54 |
| Release | : 1990 |
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| Author | : Sanjiban Chakraborty |
| Publisher | : |
| Total Pages | : 297 |
| Release | : 2011 |
| Genre | : Block copolymers |
| ISBN | : |
Block copolymers by virtue of their ability to self assemble and microphaseseparation due to the contrast in chemical and physical properties of the covalently linked blocks constitute the essential building blocks towards various nano or micro sized architectures. Polyoxometalates (POM), on the other hand, being an interesting class of metal-oxygen nanometer-sized anionic clusters, are regarded highly due to their excellent electron accepting capability. Combining POM clusters with diblock copolymers can lead to a fascinating class of hybrid materials where the POM cluster not only affect the selfassembly process of various diblock copolymers but also brings its unique electronic properties into the hybrid system. Herein we report the detailed synthesis and characterizations of two hybrid coil-coil diblock copolymers along with two hybrid rodcoil diblock copolymers through polymerization-hybridization approach. The coil-coil diblocks were synthesized via atom transfer radial polymerization (ATRP) of styryl-type monomers and 4-vinylpyridine in sequence. For rod-coil diblock copolymers, the coil block was synthesized through ATRP, followed by the conversion of the terminal bromide to an azide. Ethynyl terminated poly (p-phenylenevinylene) (PPV) and poly (3-hexylthiophene) (P3HT) were prepared separately as the rod blocks. The rod block and the coil block were connected through click chemistry to yield rod-coil diblock copolymers. After removing the phthalimide protecting groups to regenerate aryl amines, POM clusters were finally linked to the coil block of all diblock copolymers to yield the targeted hybrid diblock copolymers. The covalent cluster attachment was confirmed by UV-Vis spectroscopy, FTIR and cyclovoltammetry measurements. The structures, solution and film optical properties, self-assembled morphologies and solar cell performances of these hybrids have been studied. It has been found that solar cell devices based on hybrid P3HT exhibited rather poor performances. Fluorescence dynamic studies indicate that the photoinduced electron transfer process from the rod block to pendant POMs is quite inefficient which may account for the poor device performance. Though the self-assembly process of these hybrid diblock copolymers and the preliminary morphologies has been demonstrated, detailed and systematic study of morphological control requires further extensive research.
| Author | : Yingdong Luo |
| Publisher | : |
| Total Pages | : 183 |
| Release | : 2015 |
| Genre | : |
| ISBN | : 9781339218977 |
Block copolymer self-assembly has been used as nanopatterning towards applications of lithography for decades. For the purpose of smaller, faster and cheaper transistor developments, block copolymers with high Flory-Huggins parameter and better etching contrast need to be further developed. PDMS based block copolymers are of the most interest among all candidates. I synthesized a library of well defined PDMS-b-PMMA, PDMS-b-PS and PDMS-b-PEO through "click" chemistry. The Flory-Huggins interaction parameters of these block copolymers are characterized much higher than conventional block copolymers as expected. Therefore, sub-10 nm domain periods are achieved by these materials in bulk. Significantly, long range ordered nanoline and nanodot patterns have been produced by PDMS-b-PMMA. Furthermore, a small molecule (L)-tartaric acid used as a hydrogen bonding donor was proved to efficiently suppress the crystallinity of PEO and significantly enhance the self-assembly behavior. Finally, the triazole moiety in the middle of the block copolymer which synthesized by "click" chemistry was functionalized to produce an ionic junction block copolymer. The electrostatic interactions before the opposite charges act as an extra enthalpy to help the self-assembly. Therefore, order disorder transition temperature of the block copolymer was dramatically increased.
| Author | : Alejandra Teresa García Marcos |
| Publisher | : |
| Total Pages | : 300 |
| Release | : 2006 |
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| ISBN | : |
| Author | : Lei Feng (Chemical engineer) |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2013 |
| Genre | : Diblock copolymers |
| ISBN | : |
Block copolymers consist of two or more incompatible polymer chains linked by covalent bonds. These block copolymer can separate into nanometer sized domains whose morphology depends upon the size of the block and interactions between them. The properties of block copolymers can be modified and potentially improved by introducing noncovalent interactions to replace covalent linkages between blocks to form supramolecular block copolymers. These kinds of materials combine the microphase separation inherent to block copolymers with the facile synthesis of supramolecular materials thereby affording new and unique materials. This dissertation focuses on synthesis and characterization of PS-b-PMA block copolymers with ion-pair junctions.Firstly, the chain-end sulfonated polystyrene ([omega]-sulfonated PS) was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization and postpolymerization modification. In the postpolymerization modification two methods were investigated: in the first one, the polymer was converted to a thiol-terminated polymer by aminolysis. Then a sulfonic acid end-group was produced then by oxidation of the thiol end-group with m-chloroperoxybenzoicacid (m-CPBA); in the second method, the RAFT-polymerized polymer was directly sulfonated by oxidation with m-CPBA. After purification by column chromatography, [omega]-sulfonated PS was obtained by both methods with greater than 95% end-group functionality as measured by titration. The sulfonic acid end-group could be neutralized with various ammonium or imidazolium counter ions through acid-base or ionic metathesis reactions. These polymers with ionic end-group can be used as model supramolecular building blocks.Secondly, ammonium end functionalized polymethylacrylate (PMA) was synthesized directly by RAFT polymerization using functional RAFT agent. Then chain-end sulfonated polystyrene and ammonium end functionalized polymethylacrylate (PMA) were used to synthesize A-B block copolymers by two different methods: the first method was by mixing two oppositely charged end group functionalized polymers; the second method was to ionically bond a RAFT agent to the chain end of an end sulfonated polymer to generate a supramolecular macro RAFT agent then an A-B block copolymer was prepared by RAFT polymerization using supramolecular macro-RAFT agent. The polymerization kinetics were investigated and the molecular weight and the chemical structure of the block copolymers were characterized by 1H-NMR and SEC. The results show that the ion-bonded supramolecular block copolymer, PS-PMA, have been successfully prepared with controlled molecular weight and narrow distribution.Thirdly, the morphology of the ion-bonded supramolecular PS-PMA diblock copolymers were investigated by small-angle X-ray scattering (SAXS) and rheological techniques. Several covalently bonded PS-PMA block copolymers were synthesized by RAFT polymerization and their micro domain structures and rheology behaviors were also investigated. The results showed that the electrostatic interactions between the end ion groups are able to overcome the thermodynamic repulsion of two blocks result in the formation of diblock copolymers with similar behaviors and morphology of traditional covalent bonded diblock copolymers and their micro domain structures remain to high temperatures.
