[PDF] Synthesis Of Polyferrocenylsilane Block Copolymers And Their Crystallization Driven Self Assembly In Protic Solvents eBook

Author : Hang Zhou
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Page : pages
File Size : 44,30 MB
Release : 2018
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Polyferrocenylsilane (PFS) di-block copolymers self-assemble in selective solvents to form rod-like micelles, driven be the crystallization of the PFS block in the core. One of the unique features of these rod-like micelles is that the length can be extended upon addition of an extra amount of PFS block copolymers in a good solvent for both blocks. This process, referred to as the living crystallization-driven self-assembly (CDSA), has been utilized to prepare near monodisperse rod-like micelles. To further investigate the potential bio-medication application of these rods, I set out to synthesize new PFS BCPs with water-soluble thermoresponsive corona to prepare uniform nano-rods in polar media, and study their solution behavior. The first part of my thesis describes the synthesis and living CDSA of poly(ferrocenyldimethylsilane-b-N-isopropyl acrylamide) (PFS-b-PNIPAM) by a Cu-catalyzed alkyne/azide coupling reaction to covalently combine the two homopolymers. In self-assembly studies, I found that the growth rate of the rod-like micelles in alcohol solvents decreased dramatically when the number of PNIPAM repeating units was increased. Varies attempts to transfer the micelles to water were accompanied by extensive fragmentation. I attributed the phenomenon to the cononsolvency of PNIPAM corona in alcohol/water mixture. The second part describes the preparation of a photocleavable PFS-hv-poly(2-vinylpyridine) (P2VP) block copolymer bearing an o-nitrobenzyl ester (ONB) group at the junction. I investigated in detail the UV light-induced cleavage of the P2VP corona chains from the rod-like micelles by GPC, TEM and multiangle light scattering. The third part in the thesis describes the formation of rod-like co-micelles with segregated coronas via living CDSA of two mixed unimers of PFS-b-PNIPAM and PFS-hv-P2VP. By controlling the epitaxial growth rate of the two competing species, the morphology of the co-micelles could be varied from patchy to block co-micelles. The fourth part describes the synthesis and living CDSA of PFS-b-poly(oligo(ethylene glycol) methyl ether methacrylate) (PFS-b-POEGMA). I explored the self-assembly condition of this polymer in different alcohol media and found a methanol/ethanol mixture as selective solvent to prepare uniform nano-rods by living CDSA. These nano-rods stayed intact after transfer to water. The thermoresponsiveness of these uniform cylindrical brushes was investigated by multiangle light scattering.

Author : David Allen Rider
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Page : 598 pages
File Size : 16,48 MB
Release : 2007
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ISBN : 9780494527382

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A series of well-defined polystyrene-block-poly(ferrocenylethylmethylsilane) (PS-b-PFEMS) diblock copolymers was synthesized. Both PFEMS and PS- b-PFEMS were shown to be amorphous due to the atactic nature of the PFEMS. As a result, PS- b-PFEMS readily undergo solid-state self-assembly in the bulk producing a spectrum of ordered nanometer sized iron-rich morphologies. When cylinder-forming PS-b-PFEMSs were studied in thin films, well-ordered arrays of hexagonally packed iron-rich cylindrical microdomains oriented either parallel to or normal to the substrate were produced. The orientation was found to depend strongly on the film thickness and/or the conditions of annealing. The etching of these films using (i) reactive plasmas, and (ii) an oxidative chemical wet etch technique were investigated. Using (i), surface-patterned magnetic ceramics were produced as well as a nanotextured silver metal film. The latter was found to dramatically enhance the Raman spectroscopy of an adsorbed analyte molecule. Using (ii), nanoporous polystyrene films were generated by the quantitative elimination of PFEMS domains by exposure to a nucleophilic non-solvent under oxidizing conditions.Thin films of PS-b-PFEMS generated efficient iron nanoparticle catalysts for single-walled carbon nanotube (SWNT) growth via a chemical vapor deposition growth process. The kinetics of the formation of iron catalysts from PS- b-PFEMS and PFEMS were compared. Despite the lower iron content for PS-b -PFEMS films, more active iron sites were produced. Additionally, the tube diameter and density were tunable by adjusting the chain lengths of polyferrocenylsilane- block-polysiloxanes in thin films. Lastly, high-throughput field-effect SWNT transistors have been fabricated with more than 160 individually addressable devices on a chip.The influence of strong 3D confinement on the self-assembly of PS-b-PFEMS was studied. Both silica colloidal crystals and silica inverse colloidal crystals were used for directing the self-assembly. Unusual morphologies, such as concentric shells and branched lamellae, resulted from the interaction of the lamellar-forming PS-b-PFEMS with the high surface area templates. In addition, the control of the 3D confined morphology of cylinder-forming PS-b-PFEMS was demonstrated through mediation of the interfacial interactions within the colloidal crystal.For solution state self-assembly, PS-b -PFEMSs and polystyrene-block-poly(ferrocenylmethylphenylsilanes) (PS-b-PFEMSs) were stoichiometrically oxidized in solution. Due to a redox-induced polarity change for the PFEMS and PFMPS blocks, self-assembly into well-defined spherical micelles occurred. The micelles, composed of a core of partially oxidized PFS segments and a corona of PS, disassembled when treated with a reducing agent and regenerated unassociated free chains.Lastly, the photochemical treatment of metal-containing ferrocenophane monomers with low energy Pyrex-filtered light from a mercury lamp (lambda > 310 nm) or bright sunlight in the presence of an anionic initiator led to living polymerizations in which the conversion and molecular weight of the resulting polymer was controlled by irradiation time. The polymerization proceeded via attack of the initiator or propagating anion on the iron atom of the photoexcited monomer. The formation of functional block copolymer architectures was possible when the light is alternately switched on and off in between the sequential addition of different monomers.

Author : Victor Ho
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Page : 132 pages
File Size : 44,9 MB
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 : Nikolaos Petzetakis
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Page : pages
File Size : 28,46 MB
Release : 2012
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Chapter 1 is the main introduction of this work and it features the two main concepts of this study. First living polymerisation techniques are introduced with a special focus into RAFT and ROP. Secondly solution self-assembly is briefly discussed. In Chapter 2 we describe the synthesis of an amphiphilic block copolymer where the two blocks are connected through a reversible bond. A Diels-Alder (DA) adduct consisted of a maleimide-furan pair was chosen as the reversible linker. The solution self-assembly of this polymer was studied by TEM and DLS giving rise to the unexpected formation of cylindrical micelles. In Chapter 3 the main objective was to synthesise new amphiphilic block copolymers without the DA motif in order to investigate their self-assembly behaviour compared to those for DA containing polymers obtained in Chapter 2. To further understand this self-assembly behaviour our method has been extended to the synthesis of other hydrophilic blocks and end group modified polymers. In addition, some key properties of the polymers synthesised have been investigated. In Chapter 4 our main goal is to understand the origins of the cylindrical micelle formation seen in Chapter 2. We investigated the aggregation behaviour under the aqueous thermal conditions in which the PTHPA block hydrolysis is performed. Studies at different concentrations and solvent mixtures provide valuable information regarding the self-assembly mechanism. In addition, the polymers with modified end groups and the triblock copolymers synthesised in Chapter 3 are studied and all the results compared. In Chapter 5 we explore the living crystallisation driven self-assembly of PLA-b- PAA block copolymers in aqueous media towards the formation of cylindrical micelles of controlled length. Interestingly, in many of the unstained TEM images presented in this work the particles demonstrate a non-uniform contrast along their width. This unexpected result is fully investigated in Chapter 6.

Author : Brandon Aubrey Fultz
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Page : 0 pages
File Size : 29,92 MB
Release : 2020
Category : Chemistry
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This dissertation investigates the use of block copolymer self-assembly to create nanostructures with unique domain properties. Precise control over nanoscale feature size and properties of materials has become increasingly more important to keep up the ever-decreasing size of technology. Bottom-up approaches using block copolymers has been progressively more attractive due to their ability to autonomously self-assembly into an array of complex morphologies with features sizes as small as 2-3 nanometers. Modifications of these systems has generally been limited to only one domain as the processes under which modifications are carried out generally result in the disruption or destruction of the underlying morphology. We originally set out to create a block polymer system containing poly(vinylpyridine) (PVP) segments which can undergo several transformations such as protonation, metal coordination, or quaternization. By coupling PVP segments with poly(tert-butyl methacrylate), we believed that a well-ordered charged mosaic containing segregated opposite charges could be created without disruption of the underlying morphology. Thin films of hexagonally packed P4VP cylinders were self-assembled perpendicular to the surface and subsequently treated with bromoethane vapor at various durations to quaternize pyridinyl nitrogens. The PtBMA matrix was then partially hydrolyzed to poly(methacrylic acid), PMAA, through HCl vapor treatment followed by neutralization by brief submersion in KOH solution. Using techniques such as AFM, contact angle testing, and ToF-SIMS, we were able to determine the success of these transformations as well as methodologies in which structural morphology was maintained. An additional exploration into the use of tris(trimethylsilyl)silane (TTMSS) as non-toxic alternative to tin hydrides using only light was investigated as a method to remove reversible addition-fragmentation transfer (RAFT) chain transfer agents. As the end group removal from PVP polymers derived from RAFT has to our knowledge never been reported, we felt that these results would be invaluable to the scientific community due to the ubiquitous use of PVP in many systems. Not only was TTMSS found to be an effective reagent for RAFT removal of PVP polymers, it was also found to be effective for the removal of RAFT end groups from polystyrene which has been generally reported in literature to be difficult due to the stability of the benzyl radical. Reactions were found to be complete for most polymers in less than 2 hours whereas, other reported reagents typically took 24 hours or as much as 1 week.

Author : Mary Nell Higley
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Page : pages
File Size : 19,41 MB
Release : 2007
Category : Block copolymers
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A novel methodology has been developed for the formation of block copolymers that combines ring-opening metathesis polymerization (ROMP) with functional chain-transfer agents (CTAs), functional chain-terminators (CTs) and self-assembly. Telechelic homopolymers of cyclooctene derivatives that are end-functionalized with hydrogen-bonding or metal-coordination sites are formed via the combination of ROMP with a corresponding functional CTA. These telechelic homopolymers are fashioned with a high control over molecular weight and without the need for post-polymerization procedures. The homopolymers undergo fast and efficient self-assembly with their complement homopolymer or small molecule analogues to form block copolymer architectures. The block copolymers have similar association constants to small molecule analogues described in the literature, regardless of size or the nature of the complementary unit or the polymer side-chain. The ROMP of side-chain functionalized norbornene polymers is coupled with functional CTs to produce block copolymer with main- and side-chain self-assembly sites. Combinations of these norbornene polymers with their complement polymer via self-assembly produce non-covalent AB type block copolymers fast and efficiently. ABA type block copolymers are realized by combining the difunctional homopolymer formed via the CTA pathway with the CT synthesized mono-functional polymer. These polymers show similar association constants regardless of the sequence of polymer formation.

Author : Kristoffer Keith Stokes
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Page : 282 pages
File Size : 11,18 MB
Release : 2007
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Linear-dendritic block copolymers consisting of a poly(styrene) linear block and poly(amidoamine) dendrimer block were synthesized and examined for their ability to self-assemble in both aqueous environments and organic/aqueous mixtures. These polymers were shown to assemble into vesicle structures under a variety of conditions. Furthermore, size measurements of the dendritic portion were taken by means of Langmuir-Blodgett isotherms, demonstrating both the steric area, as well as the electrostatic area occupied by the dendrimer in a monolayer. Further studies into the rapid synthesis of such systems were also undertaken, with a particular interest in use of the so-called "click" reaction to be used as a facile means toward block copolymer synthesis.