[PDF] Synthesis Self Assembly And Modification Of Polyvinylpyridine Based Block Copolymers For The Creation Of Well Ordered Charged Nanostructures eBook

Author : Brandon Aubrey Fultz
Publisher :
Page : 0 pages
File Size : 34,62 MB
Release : 2020
Category : Chemistry
ISBN :

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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 : Gity Mir Mohamad Sadeghi
Publisher : Elsevier Inc. Chapters
Page : 121 pages
File Size : 26,76 MB
Release : 2013-11-28
Category : Technology & Engineering
ISBN : 0128090847

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Block copolymers (BCPs) consist of two or more chemically different polymers connected covalently, and are polymer alloys. Due to their thermodynamic incompatibility and chain connectivity, the phase separation between two (or more) blocks occurs only in a tens of nanometers range. Nanostructures are based on block copolymer self-assembly. They are functional nanomaterials less than 100nm in size and have received extensive scientific and technological attention due to their potential applications in electronic, biomedical, and optical materials. This chapter examines a variety of different synthetic strategies for preparation of linear diblock copolymers by anionic polymerization. Triblocks can be synthesized according to an appropriate synthetic pathway, depending on the monomers used and their sequence in the triblock chain. Nonlinear block copolymers including star block copolymers, graft copolymers, miktoarm star copolymers, cyclic block copolymers, and other complex architectures are explained. Microphase separation drives BCPs to self-assemble, resulting in ordered nanostructures, including spheres, cylinders, gyroids, and lamellae, depending on the composition of the BCP. In nanotechnology, self-assembly (SA) underlies various types of molecular structures built from nanoparticles, nanotubes, or nanorods. Supramolecular structures generated from amphiphilic block copolymers are characterized by a slow rate of intermicellar chain exchange which makes them interesting for a variety of applications. Basic principles of self-assembly and micellization of block copolymers in dilute solution, methods for stabilization of the macromolecular aggregates, are discussed. Stabilized nanoparticles, the so-called “smart materials,” which show responses to environmental changes (pH, temperature, ionic strength, etc.), are presented with a focus on their applications.

Author : Xiaojun Wang
Publisher :
Page : 250 pages
File Size : 21,53 MB
Release : 2012
Category :
ISBN :

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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 : David Allen Rider
Publisher :
Page : 598 pages
File Size : 27,57 MB
Release : 2007
Category :
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 : David H. Howe
Publisher :
Page : 127 pages
File Size : 26,43 MB
Release : 2020
Category : Block copolymers
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This thesis is focused on expanding the utility of post-polymerization modification (PPM) and establishing it as a viable route for the synthesis of self-assembled polymeric nanoparticles through three primary research projects. The first project demonstrates Pd-catalyzed, Suzuki-Miyaura cross-coupling (SMC) as a new, versatile method for PPM on well-defined polymers derived from RAFT polymerization. The second project aims to employ SMC as the driving force behind a novel strategy for inducing dynamic self-assembly of block copolymers into nanoparticles through a technique termed "functionalization induced self-assembly" (FISA). The final project of this thesis improves upon the versatility and ease-of-use of FISA by extending it to the base-catalyzed thiol-epoxide "click" reaction as the primary PPM driving in situ self-assembly, thus achieving convenient polymer nanoparticle synthesis under ambient conditions and atmosphere. Keywords: click reaction, nanoparticle, polymer, RAFT, self-assembly, Suzuki

Author : Sanchita Biswas
Publisher :
Page : 172 pages
File Size : 34,8 MB
Release : 2010
Category : Block copolymers
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Ring opening metathesis polymerization (ROMP) is established as one of the efficient controlled living polymerization methods which have various applications in polymer science and technology fields. The research presented in this dissertation addresses several applications of multifunctional well-defined norbornene-based block copolymers synthesized by ROMP using ruthenium-based Grubbs catalysts. These novel block copolymers were applied to stabilize maghemite nanoparticles, creating the superparamagnetic polymeric nanocomposites. The J-aggregation properties of the porphyrin dyes were improved via self-assembly with a customized norbornene polymer. Novel multimodal copolymer probes were synthesized for two-photon fluorescence integrin-targeted bioimaging. In Chapter 1 a brief overview of ROMP along with ruthenium metal catalysts and selected applications of the polymers related to this research is presented. Superparamagnetic maghemite nanoparticles are important in biotechnology fields, such as enhanced magnetic resonance imaging (MRI), magnetically controlled drug delivery, and biomimetics. However, cluster formation and eventual loss of nano-dimensions is a major obstacle for these materials. Chapter 2 presents a solution to this problem through nanoparticles stabiulized in a polymer matrix. The synthesis and chracterization of novel diblock copolymers, consisting of epoxy pendant anchoring groups to chelate maghemite nanoparticles and steric stabilizing groups, as well as generation of nanocomposites and their characterization, including surface morphologies and magnetic properties, is discussed in Chapter 2. In Chapter 3, further improvement of the nanocomposites by ligand modification and the synthesis of pyrazole-templated diblock copolymers and their impact to stabilize the maghemite nanocomposite are presented. Additionally, the organic soluble magnetic nanocomposites with high magnetizations were encapsulated in an amphiphilic copolymer and dispersed in water to assess their water stability by TEM. To gain a preliminary measure of biocopatibility of the micelle-encapsulated polymeric magnetic nanocomposites, cell-viability was determined. In Chapter 4, aggregation behaviors of two porphyrin-based dyes were investigated. A new amphiphilic homopolymer containing secondary amine moieties was synthesized and characterized. In low pH, the polymer became water soluble and initiated the stable J-aggregation of the porphyrin. Spectroscopic data supported the aggregation behavior. Two photon fluorescence microscopy (2PFM) has become a powerful technique in bioimaging for non-invasive imaging and potential diagnosis and treatment of a number of diseases via excitation in the near-infrared (NIR) region. The fluorescence emission upon two-photon absorption (2PA) is quadratically dependent with the intensity of excitation light (compared to the linear dependence in the case of one-photon absoprtion), offering several advantages for biological applications over the conventional one-photon absorption (1PA) due to the high 3D spatial resolution that is confined near the focal point along with less photodamage and interference from the biological tissues at longer wavelength (~700-900 nm). Hence, efficient 2PA absorbing fluorophores conjugated with specific targeting moieties provides an even better bioimaging probe to diagnose desired cellular processes or areas of interest The [alpha subscript v beta subscript 3] integrin adhesive protein plays a significant role in regulating angiogenesis and is over-expressed in uncontrolled neovascularization during tumor growth, invasion, and metastasis. Cyclic-RGD peptides are well-known antagonists of [alpha subscript v beta subscript 3] integrin which suppress the angiogenesis process, thus preventing tumor growth. In Chapter 5 the synthesis, photophysical studies and bioimaging is reported for a versatile norbornene-based block copolymer multifunctional scaffold containing biocompatible (PEG), two-photon fluorescent (fluorenyl), and targeting (cyclic RGD peptide) moieties. This water-soluble polymeric multi scaffold probe with negligible cytotoxicity exhibited much stronger fluorescence and high localization in U87MG cells (that overexpress integrin) compared to control MCF7 cells. The norbornene-based polymers and copolymers have quite remarkable versatility for the creation of advanced functional magnetic, photonic, and biophotonic materials.

Author : Yingdong Luo
Publisher :
Page : 183 pages
File Size : 12,21 MB
Release : 2015
Category :
ISBN : 9781339218977

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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 : Li Yao
Publisher :
Page : 150 pages
File Size : 14,86 MB
Release : 2014
Category : Block copolymers
ISBN :

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This dissertation explores the use of block copolymers which can self-assemble into different morphologies as templates to fabricate nanostructured materials. The first section (Chapters 2-4) reports the formation of mesoporous silica films with spherical, cylindrical and bicontinuous pores up to 40 nm in diameter through replicating the morphologies of the solid block copolymer (BCP) templates, polystyrene-b-poly(tert-butyl acrylate) (PS-b-PtBA), via phase selective condensation of tetraethylorthosilicate in supercritical CO2. Next, directed self-assembly was used to control the orientation of cylindrical domains in PS-b-PtBA templates. Large-area aligned mesochannels in silica films with diameters tunable between 5 and 30 nm were achieved through the replication of oriented templates via scCO2 infusion. The long-range alignment of mesochannels was confirmed through GISAXS with sample stage azimuthal rotation. In the second section (Chapters 5-6), enantiopure tartaric acid was used as an additive to dramatically improve ordering in poly(ethylene oxide-block-tert-butyl acrylate) (PEO-b-PtBA) copolymers. Transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray scattering were used to study the phase behavior and morphologies within both bulk and thin films. With the addition of a photo acid generator, photo-induced disorder in the PEO-b-PtBA/tartaric acid composite system was achieved upon UV exposure which deprotected the PtBA block to yield poly(acrylic acid) (PAA), which is phase-miscible with PEO. Area-selective UV exposure using a photo-mask was applied with the assistance of trace amounts of base quencher to achieve high-resolution hierarchical patterns. Helical superstructures were observed by TEM in this BCP/chiral additive system with 3D handedness confirmed by TEM tomography. In the last section (Chapter 7), ultra-high loadings of nanoparticles into target domains of block copolymer composites were achieved by blending the block copolymer hosts with small molecule additives that exhibit strong interactions with one of the polymer chain segments and with the nanoparticle ligands via hydrogen bonding. The addition of 40 wt% D-tartaric acid to poly(ethylene oxide-block-tert-butyl acrylate) (PEO-b-PtBA) enabled the loading of up to 150 wt% of 4-hydroxythiophenol functionalized Au nanoparticles relative to the mass of the target hydrophilic domain. This was equivalent to over 40% Au by mass of the resulting well ordered composite as measured by thermal gravimetric analysis.