Cyclic Polymers
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Cyclic Polymers
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Author : E.R. Semlyen
language : en
Publisher: Springer Science & Business Media
Release Date : 2012-12-06
Cyclic Polymers written by E.R. Semlyen and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-12-06 with Technology & Engineering categories.
Synthetic polymers based on long chain molecules have been investigated intensively for over 50 years. They have found important applications as plastics, fibres, rubbers and other materials. The chain molecules may be simple linear structures or they may be branched or cross-linked. During the past decade, sharp fractions of the first synthetic cyclic polymer have been prepared. These fractions of cyclic poly(dimethyl siloxane) consist of ring molecules containing hundreds of skeletal bonds. Some of their properties have been found to be quite different from those of the corresponding linear polymers. Synthetic cyclic polymers, including cyclic polystyrene, have joined the naturally occurring circular DNAs as examples of substantially large ring molecules. This book aims to review current knowledge of cyclic polymers and biological ring macromolecules. In addition, it discusses theories of cyclic macromolecules and describes cyclization processes involving long chain molecules. Since 1865, when Kekule proposed a simple ring structure for benzene, larger and larger ring molecules have been synthesized in the laboratory and discovered in nature. Many more examples are to be expected in the future. In time, large ring molecules should take their proper place alongside long chain molecules as one of the two possible constituent structural units of polymers.
Cyclic Polymers
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Author : E.R. Semlyen
language : en
Publisher: Springer Science & Business Media
Release Date : 2007-05-08
Cyclic Polymers written by E.R. Semlyen and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007-05-08 with Technology & Engineering categories.
Cyclic Polymers (Second Edition) reviews the many recent advances in this rapidly expanding subject since the publication of the first edition in 1986. The preparation, characterisation, properties and applications of a wide range of organic and inorganic cyclic oligomers and polymers are described in detail, together with many examples of catenanes and rotaxanes. The importance of large cyclics in biological chemistry and molecular biology is emphasised by a wide coverage of circular DNA, cyclic peptides and cyclic oligosaccharides and polysaccharides. Experimental techniques and theoretical aspects of cyclic polymers are included, as well as examples of their uses such as ring opening polymerisation reactions to give commercially important materials. This book covers a wide range of topics which should be of interest to many scientific research workers (for example, in polymer science, chemistry and molecular biology), as well as providing a reference text for undergraduate and graduate students.
Topological Polymer Chemistry
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Author : Yasuyuki Tezuka
language : en
Publisher: World Scientific
Release Date : 2013
Topological Polymer Chemistry written by Yasuyuki Tezuka and has been published by World Scientific this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with Mathematics categories.
There are examples aplenty in the macroscopic world that demonstrate the form of objects directing their functions and properties. On the other hand, the fabrication of extremely small objects having precisely defined structures has only recently become an attractive challenge, which is now opening the door to nanoscience and nanotechnology. In the field of synthetic polymer chemistry, a number of critical breakthroughs have been achieved during the first decade of this century to produce an important class of polymers having a variety of cyclic and multicyclic topologies. These developments now offer unique opportunities in polymer materials design to create unprecedented properties and functions simply based on the form, i.e. topology, of polymer molecules. In this book on topological polymer chemistry, the important developments in this growing area will be collected for the first time, with particular emphasis on new conceptual insights for polymer chemistry and polymer materials. The book will systematically review topological polymer chemistry from basic aspects to practice, and give a broad overview of cyclic polymers covering new synthesis, structure characterization, basic properties/functions and the eventual applications.
Cyclic Polymers
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Author : E. R. Semlyen
language : en
Publisher:
Release Date : 2014-01-15
Cyclic Polymers written by E. R. Semlyen and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014-01-15 with categories.
Cyclic Polymers
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Author : J. A. Semlyen
language : en
Publisher: Springer Science & Business Media
Release Date : 2000-08-31
Cyclic Polymers written by J. A. Semlyen and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2000-08-31 with Science categories.
Cyclic Polymers (Second Edition) reviews the many recent advances in this rapidly expanding subject since the publication of the first edition in 1986. The preparation, characterisation, properties and applications of a wide range of organic and inorganic cyclic oligomers and polymers are described in detail, together with many examples of catenanes and rotaxanes. The importance of large cyclics in biological chemistry and molecular biology is emphasised by a wide coverage of circular DNA, cyclic peptides and cyclic oligosaccharides and polysaccharides. Experimental techniques and theoretical aspects of cyclic polymers are included, as well as examples of their uses such as ring opening polymerisation reactions to give commercially important materials. This book covers a wide range of topics which should be of interest to many scientific research workers (for example, in polymer science, chemistry and molecular biology), as well as providing a reference text for undergraduate and graduate students.
N Heterocyclic Carbene Mediated Zwitterionic Polymerization For Cyclic Polymers
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Author : Eun Ji Shin
language : en
Publisher:
Release Date : 2011
N Heterocyclic Carbene Mediated Zwitterionic Polymerization For Cyclic Polymers written by Eun Ji Shin 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.
Zwitterionic polymerization involves a propagating species with both positively and negatively charged groups. Previous investigations on zwitterionic polymerization concern alternating copolymerization of nucleophilic and electrophilic monomers and polymerization of isolated stable zwitterionic monomers. More recently, the ring-opening polymerization of cyclic monomers using nucleophilic initiators have been studied. Specifically, the zwitterionic polymerization of cyclic esters using N-heterocyclic carbenes (NHCs) is the focus of this thesis. The N-heterocyclic carbene mediated zwitterionic polymerization of cyclic monomers provides an expedient route to polymers of various architectures, such as cyclic polymers, cyclic gradient copolymers and linear telechelic polymers. The ring-opening polymerization of lactide initiated by NHCs generates cyclic poly(lactide)s of defined molecular weight and molecular weight distribution. Kinetic studies implicate a mechanism that involves a slow initiation step and a propagation step that is much faster than depropagation and chain termination by cyclization. Stochastic simulations and chain extension experiments showed that only a fraction of the NHC forms the active zwitterion in solution, leading to both chain extension of the zwitterions and re-initiation of the NHC upon addition of the second batch of monomer. These results prompted investigation of a more efficient way to prepare cyclic block copolymers. The difference in reactivity of NHCs towards different monomers was exploited to synthesize cyclic block copolymers of valerolactone (VL) and caprolactone (CL). The faster ring-opening of VL relative to CL resulted in a gradient cyclic copolymer comprised of VL-rich sequences that transition to CL-rich sequences in a cyclic macromolecule, instead of a cyclic diblock copolymer. This work not only provides a simple batch copolymerization protocol to produce cyclic gradient copolymers, but also demonstrates the marked difference in reactivity of the NHCs compared to metal catalysts, which produce random copolymers. Stereocomplexation behavior has been observed in blends of linear poly(L-lactide) and linear poly(D-lactide). The influence of topology on the formation of stereocomplex was investigated using blends of linear and cyclic poly(lactide)s prepared by NHC mediated zwitterionic polymerization. The linear/cyclic and cyclic/cyclic blends all form stereocomplexes when annealed. Analyses of data from various characterization techniques indicate that the cyclic topology imposes constraints on the stereocomplexation formation. The purity of the cyclic polymers is always a concern in the synthesis and physical property studies. Attempts to identify and quantify the linear contamination in cyclic poly(caprolactone) samples are described. Esterification reactions targeting the hydroxyl endgroups of linear contaminants were not successful, but the macroinitiator approach where the linear contaminant in a cyclic polymer sample is used as the macroinitiator to grow polymers to identify and remove the linear contamination shows promise. A cyclic polymer more robust to post-polymerization chemistry may be needed for more thorough purity studies.
Zwitterionic Polymerization For The Synthesis Of High Molecular Weight Cyclic Polymers
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Author : Hayley A. Brown
language : en
Publisher:
Release Date : 2013
Zwitterionic Polymerization For The Synthesis Of High Molecular Weight Cyclic Polymers written by Hayley A. Brown and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.
Topological isomerism in macromolecules represents a fascinating field of study. Linear polymers form the basis of much of the current scientific understanding of bulk polymer behavior due to their simple structure and synthetic accessibility. In contrast, cyclic polymers remain poorly understood due to the difficulty in generating sufficient quantities of pure samples; in particular, high molecular weight samples where phenomena related to entanglement could be observed have eluded polymer chemists until recently. Among the several strategies employed for the synthesis of high molecular weight cyclic polymers, recent reports have highlighted the utility of zwitterionic ring-opening polymerization (ZROP). Efforts to understand the N-heterocyclic carbene (NHC) mediated ring-opening of strained lactones have led to the development of several mechanistic models. Kinetic studies on the NHC-mediated polymerization of [epsilon]-caprolactone (CL) and [delta]-valerolactone (VL) were conducted to account for the notably high molecular weight cyclic polyerms generated. While the two monomer systems are closely related and polymerize with the same NHC initiators, a difference in the dependence of the reaction rate on monomer is observed. A general mechanism is proposed for the polymerization of VL. Exploiting the utility of ZROP to generate high molecular weight poly([epsilon]-caprolactone) allowed for a comparative study on the bulk crystallization of cyclic PCL and linear PCL across a range of molecular weights. WAXS and SAXS studies show that linear and cyclic PCL exhibit the same global and local crystalline structure but that cyclic PCL crystallizes more rapidly than linear PCL. Isothermal DSC crystallization kinetic studies support this observation and indicate that the difference in crystallization rate increases with increasing molecular weight. Approximating the equilibrium melting temperature of these samples using the Hoffmann-Weeks method indicates that there is no significant difference in Tm0 between cyclic and linear PCL. In an attempt to broaden the scope of initiators for the ZROP of strained lactones, the use of amidines for the polymerization of lactide was explored. 1,8-Diazabicyclo[5.4.0] undec-7-ene (DBU) and 1,5-Diazabicyclo[4.3.0]non-5-ene (DBN) were shown to mediate the ZROP of lactide to give predominantly cyclic poly(lactide) (PLA). A notable solvent effect with no polymerization occurring in neat tetrahydrofuran (THF), fast polymerization with formation of significant amounts of linear PLA in dichloromethane (DCM), and moderate rate of polymerization with minimal formation of linear PLA in THF:DCM blends. DFT computations suggest that the formation of a neutral tricyclic species, a zwitterionic species, and a ketene-aminal are energetically feasible. This ketene-aminal is thought to be the source of the linear PLA observed. Our efforts to develop a more hydrolytically stable family of cyclic polymers led to the investigation of the ZROP of strained cyclic carbosiloxanes. NHC-mediated polymerization of 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane occurs rapidly to give polymers with molecular weights exceeding 106 g/mol. While these polymerizations are difficult to control, the cyclic topology of the resulting polymers could be confirmed by comparative dilute solution viscosity studies and MALDI-TOF MS. As a complimentary strategy to the use of neutral nucleophiles to initiate anionic-like zwitterionic polymerization, neutral Lewis acids were tested for the electrophilic zwitterionic ring opening polymerization (EZROP) of strained heterocycles. Polymerization of 2-ethyl-2-oxaline proceeds slowly at elevated temperature with boron-based Lewis acids to give HF-capped linear chains, determined by MALDI-TOF MS. In contrast, the polymerization of 3,3-dimethyloxetane proceeds very rapidly at room temperature with B(C6F5)3 to give a mixture of polymer products likely resulting from methyl scrambling between chains.
The Preparation And Properties Of Some Cyclic Polymers
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Author : Robert Dadd Campling Richards
language : en
Publisher:
Release Date : 1988
The Preparation And Properties Of Some Cyclic Polymers written by Robert Dadd Campling Richards and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1988 with categories.
Cyclic Polymers
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Author : J.A. Semlyen (ed)
language : en
Publisher:
Release Date :
Cyclic Polymers written by J.A. Semlyen (ed) and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on with categories.
Part I
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Author : George Robert McKeown
language : en
Publisher:
Release Date : 2020
Part I written by George Robert McKeown and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with categories.
This thesis is presented in two parts. Part I begins with an introduction to some contemporary problems in polymer chemistry, but also contains what is essentially a mini-review of catalyst transfer polymerization (CTP). This part of the chapter elucidates a number of common misunderstandings of CTP that are present in the literature. It goes onto suggest a new set of design principles to design new CTP systems for a wider variety of monomers. This leads into the first homogenous synthesis of monodisperse polymers. Through cycling between low and high temperatures and carefully controlling monomer activation, we show that it is possible to add exactly one monomer per temperature cycle to each chain in solution, resulting in monodisperse polymers with quantitatively controlled end groups. Part I also describes a project in which macrocyclic poly(3-hexylthiophene) (P3HT) and poly(3-heptylselenophene) (P37S) were synthesized from their linear counterparts. The approach used to accomplish this differs from more common syntheses of cyclic polymers, in that the relatively long persistence length of the polymers makes it unreasonable to assume 100\% cyclization. The approach presented in this chapter is meant to be as general as possible, and to have applications in other cases where polymers need to be separated based on chemical functionality. Part II is an introduction to dipyrromethene and aza-dipyrromethene dyes, along with common methods for their syntheses. It goes on to present a new synthesis of aza-dipyrromethene dyes, which provides an easy route to a number of previously inaccessible compounds, as the previously existing procedures for these dyes are very limited. During the course of this project, it was discovered that one of the starting materials reacted under the same conditions to give a completely different major product. Understanding the mechanism through which it is produced may enable the development of a previously unknown chemical transformation.