Synthesis And Solution State Self Assembly Of Linear Dendritic Block Copolymers
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Synthesis And Solution State Self Assembly Of Linear Dendritic Block Copolymers
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Author : Kristoffer Keith Stokes
language : en
Publisher:
Release Date : 2007
Synthesis And Solution State Self Assembly Of Linear Dendritic Block Copolymers written by Kristoffer Keith Stokes and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007 with categories.
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.
Synthesis Characterization And Self Assembly Of Amphiphilic Block Copolymers
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Author : Xiaojun Wang
language : en
Publisher:
Release Date : 2012
Synthesis Characterization And Self Assembly Of Amphiphilic Block Copolymers written by Xiaojun Wang and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.
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.
Synthesis And Self Assembly Of Multiple Thermoresponsive Amphiphilic Block Copolymers
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Author : Jan Weiss
language : en
Publisher:
Release Date : 2011
Synthesis And Self Assembly Of Multiple Thermoresponsive Amphiphilic Block Copolymers written by Jan Weiss and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
In the present thesis, the self-assembly of multi thermoresponsive block copolymers in dilute aqueous solution was investigated by a combination of turbidimetry, dynamic light scattering, TEM measurements, NMR as well as fluorescence spectroscopy. The successive conversion of such block copolymers from a hydrophilic into a hydrophobic state includes intermediate amphiphilic states with a variable hydrophilic-to-lipophilic balance. As a result, the self-organization is not following an all-or-none principle but a multistep aggregation in dilute solution was observed. The synthesis of double thermoresponsive diblock copolymers as well as triple thermoresponsive triblock copolymers was realized using twofold-TMS labeled RAFT agents which provide direct information about the average molar mass as well as residual end group functionality from a routine proton NMR spectrum. First a set of double thermosensitive diblock copolymers poly(N-n-propylacrylamide)-b-poly(N-ethylacrylamide) was synthesized which differed only in the relative size of the two blocks. Depending on the relative block lengths, different aggregation pathways were found. Furthermore, the complementary TMS-labeled end groups served as NMR-probes for the self-assembly of these diblock copolymers in dilute solution. Reversible, temperature sensitive peak splitting of the TMS-signals in NMR spectroscopy was indicative for the formation of mixed star-/flower-like micelles in some cases. Moreover, triple thermoresponsive triblock copolymers from poly(N-n-propylacrylamide) (A), poly(methoxydiethylene glycol acrylate) (B) and poly(N-ethylacrylamide) (C) were obtained from sequential RAFT polymerization in all possible block sequences (ABC, BAC, ACB). Their self-organization behavior in dilute aqueous solution was found to be rather complex and dependent on the positioning of the different blocks within the terpolymers. Especially the localization of the low-LCST block (A) had a large influence on the aggregation behavior. Above the first cloud point, aggregates were only observed when the A block was located at one terminus. Once placed in the middle, unimolecular micelles were observed which showed aggregation only above the second phase transition temperature of the B block. Carrier abilities of such triple thermosensitive triblock copolymers tested in fluorescence spectroscopy, using the solvatochromic dye Nile Red, suggested that the hydrophobic probe is less efficiently incorporated by the polymer with the BAC sequence as compared to ABC or ACB polymers above the first phase transition temperature. In addition, due to the problem of increasing loss of end group functionality during the subsequent polymerization steps, a novel concept for the one-step synthesis of multi thermoresponsive block copolymers was developed. This allowed to synthesize double thermoresponsive di- and triblock copolymers in a single polymerization step. The copolymerization of different N-substituted maleimides with a thermosensitive styrene derivative (4-vinylbenzyl methoxytetrakis(oxyethylene) ether) led to alternating copolymers with variable LCST. Consequently, an excess of this styrene-based monomer allowed the synthesis of double thermoresponsive tapered block copolymers in a single polymerization step.
Click Polymerization
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Author : Anjun Qin
language : en
Publisher: Royal Society of Chemistry
Release Date : 2018-08-28
Click Polymerization written by Anjun Qin and has been published by Royal Society of Chemistry this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-08-28 with Science categories.
Click chemistry describes organic reactions which are highly efficient, regioselective and allow for mild reaction conditions. The archetypal click reaction of Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is used in many diverse areas and has been extensively developed for polymer synthesis, leading to the term of click polymerization. This technique enables the preparation of functional polymers with linear and topological structures that have the potential to be used in optoelectronics and biological fields. Edited by world renowned experts, Click Polymerization is the first book to comprehensively summarize this approach to polymer synthesis consolidating all the different reaction types in one resource. From the basic knowledge through to the latest developments in synthesis, chapters include transition-metal catalysed and metal-free azide-alkyne click polymerizations as well as thiol-ene, thiol-yne and thiol-epoxy click polymerizations. The book provides an authoritative guide to click polymerization techniques for graduate students and researchers interested in polymer chemistry and materials science.
Synthesis Self Assembly And Modification Of Poly Vinylpyridine Based Block Copolymers For The Creation Of Well Ordered Charged Nanostructures
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Author : Brandon Aubrey Fultz
language : en
Publisher:
Release Date : 2020
Synthesis Self Assembly And Modification Of Poly Vinylpyridine Based Block Copolymers For The Creation Of Well Ordered Charged Nanostructures written by Brandon Aubrey Fultz and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with Chemistry categories.
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.
Self Assembly Of Linear Dendritic Diblock Copolymers
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Author : Mark Alan Johnson
language : en
Publisher:
Release Date : 2002
Self Assembly Of Linear Dendritic Diblock Copolymers written by Mark Alan Johnson and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2002 with categories.
Linear-dendritic diblock copolymers combine the properties of dendritic macromolecules with the morphology of block copolymers, making it possible to create nanostructured materials which self assemble in the bulk state to form ordered thin films, and in solution to form highly functional micellar systems. The linear-dendritic system described here consists of 2000 molecular weight linear polyethylene oxide (PEO) with a polyamidoamine (PAMAM) dendron covalently bonded to one chain end. Specular neutron reflectivity has been used to investigate the structure of monolayers formed at an air-water interface. The dendritic end groups were functionalized with deuterated stearic acid to make the dendritic block hydrophobic, resulting in a macroamphiphile. Results indicate that stable monolayers are formed with PEO resting on the subphase and stearate groups extending into the air. Surface concentration and dendrimer generation were both found to impact monolayer formation.
Miktoarm Star Polymers
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Author : Ashok Kakkar
language : en
Publisher: Royal Society of Chemistry
Release Date : 2017-04-13
Miktoarm Star Polymers written by Ashok Kakkar and has been published by Royal Society of Chemistry this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017-04-13 with Technology & Engineering categories.
The term ‘miktoarm polymers’ refers to asymmetric branched macromolecules, a relatively new entry to the macromolecular field. Recent advances in their synthesis and intriguing supramolecular chemistry in a desired medium has seen a fast expansion of their applications. The composition of miktoarm polymers can be tailored and even pre-defined to allow a desired combination of functions, meaning polymer chemists can have complete control of the overall architecture of these macromolecules. By carefully selecting the composition, they can create supramolecular structures with intriguing properties, particularly for applications in biology. Miktoarm Star Polymers features chapters from experts actively working in this field, and provides the reader with a unique introduction to the fundamental principles of this exciting macromolecular system. Topics covered include the design, synthesis, characterization, self-assembly and applications of miktoarm polymers. The book is an excellent overview and up to date guide to those working in research in polymer chemistry, materials science, and polymers for medical applications.
Synthesis And Characterization Of Stimuli Responsive Block Copolymers Self Assembly Behavior And Applications
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Author : Michael Duane Determan
language : en
Publisher:
Release Date : 2006
Synthesis And Characterization Of Stimuli Responsive Block Copolymers Self Assembly Behavior And Applications written by Michael Duane Determan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
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.
Synthesis And Characterization Of Stimuli Responsive Block Copolymers Self Assembly Behavior And Applications
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Author :
language : en
Publisher:
Release Date : 2005
Synthesis And Characterization Of Stimuli Responsive Block Copolymers Self Assembly Behavior And Applications written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005 with categories.
The central theme of this thesis work is to develop new block copolymer materials for biomedical applications. While there are many reports of stimuli-responsive amphiphilic [19-21] and crosslinked hydrogel materials [22], the development of an in situ gel forming, pH responsive pentablock copolymer is a novel contribution to the field, Figure 1.1 is a sketch of an ABCBA pentablock copolymer. The A blocks are cationic tertiary amine methacrylates blocked to a central Pluronic F127 triblock copolymer. In addition to the prerequisite synthetic and macromolecular characterization of these new materials, the self-assembled supramolecular structures formed by the pentablock were experimentally evaluated. This synthesis and characterization process serves to elucidate the important structure property relationships of these novel materials, The pH and temperature responsive behavior of the pentablock copolymer were explored especially with consideration towards injectable drug delivery applications. Future synthesis work will focus on enhancing and tuning the cell specific targeting of DNA/pentablock copolymer polyplexes. The specific goals of this research are: (1) Develop a synthetic route for gel forming pentablock block copolymers with pH and temperature sensitive properties. Synthesis of these novel copolymers is accomplished with ATRP, yielding low polydispersity and control of the block copolymer architecture. Well defined macromolecular characteristics are required to tailor the phase behavior of these materials. (2) Characterize relationship between the size and shape of pentablock copolymer micelles and gel structure and the pH and temperature of the copolymer solutions with SAXS, SANS and CryoTEM. (3) Evaluate the temperature and pH induced phase separation and macroscopic self-assembly phenomenon of the pentablock copolymer. (4) Utilize the knowledge gained from first three goals to design and formulate drug delivery formulations based on the multi-responsive properties of the pentablock copolymer. Demonstrate potential biomedical applications of these materials with in vitro drug release studies from pentablock copolymer hydrogels. The intent of this work is to contribute to the knowledge necessary for further tailoring of these, and other functional block copolymer materials for biomedical applications.
Self Assembly Behavior In Hydrophilic Block Copolymers
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Author : Clara Valverde Serrano
language : en
Publisher:
Release Date : 2011
Self Assembly Behavior In Hydrophilic Block Copolymers written by Clara Valverde Serrano and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
Block copolymers are receiving increasing attention in the literature. Reports on amphiphilic block copolymers have now established the basis of their self-assembly behavior: aggregate sizes, morphologies and stability can be explained from the absolute and relative block lengths, the nature of the blocks, the architecture and also solvent selectiveness. In water, self-assembly of amphiphilic block copolymers is assumed to be driven by the hydrophobic. The motivation of this thesis is to study the influence on the self-assembly in water of A b B type block copolymers (with A hydrophilic) of the variation of the hydrophilicity of B from non-soluble (hydrophobic) to totally soluble (hydrophilic). Glucose-modified polybutadiene-block-poly(N-isopropylacrylamide) copolymers were prepared and their self-assembly behavior in water studied. The copolymers formed vesicles with an asymmetric membrane with a glycosylated exterior and poly(N-isopropylacrylamide) on the inside. Above the low critical solution temperature (LCST) of poly(N-isopropylacrylamide), the structure collapsed into micelles with a hydrophobic PNIPAM core and glycosylated exterior. This collapse was found to be reversible. As a result, the structures showed a temperature-dependent interaction with L-lectin proteins and were shown to be able to encapsulate organic molecules. Several families of double hydrophilic block copolymers (DHBC) were prepared. The blocks of these copolymers were biopolymers or polymer chimeras used in aqueous two-phase partition systems. Copolymers based on dextran and poly(ethylene glycol) blocks were able to form aggregates in water. Dex6500-b-PEG5500 copolymer spontaneously formed vesicles with PEG as the "less hydrophilic" barrier and dextran as the solubilizing block. The aggregates were found to be insensitive to the polymer's architecture and concentration (in the dilute range) and only mildly sensitive to temperature. Variation of the block length, yielded different morphologies. A longer PEG chain seemed to promote more curved aggregates following the inverse trend usually observed in amphiphilic block copolymers. A shorter dextran promoted vesicular structures as usually observed for the amphiphilic counterparts. The linking function was shown to have an influence of the morphology but not on the self-assembly capability in itself. The vesicles formed by dex6500-b-PEG5500 showed slow kinetics of clustering in the presence of Con A lectin. In addition both dex6500-b-PEG5500 and its crosslinked derivative were able to encapsulate fluorescent dyes. Two additional dextran-based copolymers were synthesized, dextran-b-poly(vinyl alcohol) and dextran-b-poly(vinyl pyrrolidone). The study of their self-assembly allowed to conclude that aqueous two-phase systems (ATPS) is a valid source of inspiration to conceive DHBCs capable of self-assembling. In the second part the principle was extended to polypeptide systems with the synthesis of a poly(N-hydroxyethylglutamine)-block-poly(ethylene glycol) copolymer. The copolymer that had been previously reported to have emulsifying properties was able to form vesicles by direct dissolution of the solid in water. Last, a series of thermoresponsive copolymers were prepared, dextran-b-PNIPAMm. These polymers formed aggregates below the LCST. Their structure could not be unambiguously elucidated but seemed to correspond to vesicles. Above the LCST, the collapse of the PNIPAM chains induced the formation of stable objects of several hundreds of nanometers in radius that evolved with increasing temperature. The cooling of these solution below LCST restored the initial aggregates. This self-assembly of DHBC outside any stimuli of pH, ionic strength, or temperature has only rarely been described in the literature. This work constituted the first formal attempt to frame the phenomenon. Two reasons were accounted for the self-assembly of such systems: incompatibility of the polymer pairs forming the two blocks (enthalpic) and a considerable solubility difference (enthalpic and entropic). The entropic contribution to the positive Gibbs free energy of mixing is believed to arise from the same loss of conformational entropy that is responsible for "the hydrophobic effect" but driven by a competition for water of the two blocks. In that sense this phenomenon should be described as the "hydrophilic effect".