Zwitterionic Polymerization For The Synthesis Of High Molecular Weight Cyclic Polymers
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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.
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.
Synthesis And Properties Of Large Ring Macromolecules
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Author : Wonhee Jeong
language : en
Publisher:
Release Date : 2008
Synthesis And Properties Of Large Ring Macromolecules written by Wonhee Jeong and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with categories.
Polymer Synthesis Theory And Practice
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Author : Dietrich Braun
language : en
Publisher: Springer Science & Business Media
Release Date : 2013-06-29
Polymer Synthesis Theory And Practice written by Dietrich Braun 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 2013-06-29 with Technology & Engineering categories.
This Laboratory Manual contains detailed descriptions for the synthesis and characterization of macromolecules. Around 110 elaborated examples, consisting of descriptions of experiments, as well as sufficient theoretical explanations enable the reader to learn about the syntheses, modification, characterization and properties of polymers including recent developments. All experiments can be conducted with adequate laboratory equipment. Suitable for students in organic and polymer chemistry as well as for chemists in industry who want to acquaint themselves with the theoretical and practical aspects of macromolecular chemistry.
New Methods Of Polymer Synthesis
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Author : J.R. Ebdon
language : en
Publisher: Springer Science & Business Media
Release Date : 2012-12-06
New Methods Of Polymer Synthesis written by J.R. Ebdon 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.
Few polymer chemists have much familiarity with recent developments in the synthesis of speciality polymers. This volume provides up-to-date reviews of areas of current interest and is directed at polymer chemists in the academic world and industry.
Synthesis Of Polymers
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Author : Dieter A. Schlüter
language : en
Publisher: John Wiley & Sons
Release Date : 2012-05-14
Synthesis Of Polymers written by Dieter A. Schlüter and has been published by John Wiley & Sons this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-05-14 with Science categories.
Polymers are huge macromolecules composed of repeating structural units. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials. Due to the extraordinary range of properties accessible, polymers have come to play an essential and ubiquitous role in everyday life - from plastics and elastomers on the one hand to natural biopolymers such as DNA and proteins on the other hand. The study of polymer science begins with understanding the methods in which these materials are synthesized. Polymer synthesis is a complex procedure and can take place in a variety of ways. This book brings together the "Who is who" of polymer science to give the readers an overview of the large field of polymer synthesis. It is a one-stop reference and a must-have for all Chemists, Polymer Chemists, Chemists in Industry, and Materials Scientists.
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.
Polymer Synthesis
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Author : Stanley R. Sandler
language : en
Publisher: Gulf Professional Publishing
Release Date : 1992
Polymer Synthesis written by Stanley R. Sandler and has been published by Gulf Professional Publishing this book supported file pdf, txt, epub, kindle and other format this book has been release on 1992 with Science categories.
This revised and updated second edition of Polymer Syntheses, Volume I brings together useful preparative methods for polymers and resins by functional group type that are of interest to both academic and industrial researchers. Several new directions for polymerization procedures have been included and are organized by various methodologies. Tables of physical property data and preparations make this book a valuable addition to any research library or research group. Provides detailed directions for the synthesis of various functional groups Includes up-to-date references to the journal literature and patents (foreign and domestic) Reviews the chemistry for each functional group and suggests where additional research is needed
New Methods Polymer Synthesis
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Author : J. R. Ebdon
language : en
Publisher: Springer Science & Business Media
Release Date : 2012-12-06
New Methods Polymer Synthesis written by J. R. Ebdon 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 Science categories.
Most practitioners and students of polymer chemistry are familiar, in general terms at least, with the established methods of polymer synthesis - radical, anionic, cationic and coordination addition polymerization, and stepwise con densation and rearrangement polymerization. These methods are used to synthesize the majority of polymers used in the manufacture of commercially important plastics, fibres, resins and rubbers, and are covered in most introduc tory polymer chemistry textbooks and in most undergraduate and graduate courses on polymer science. Fewer polymer chemists, however, have much familiarity with more recent developments in methods of polymer synthesis, unless they have been specifically involved for some time in the synthesis of speciality polymers. These developments include not only refinements to established methods but also new mechanisms of polymerization, such as group transfer and metathesis polymerization and novel non-polymerization routes to speciality polymers involving, for example, the chemical modification of preformed polymers or the linking together of short terminally functionalized blocks.
Handbook Of Polymer Synthesis
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Author : Hans R. Kricheldorf
language : en
Publisher: CRC Press
Release Date : 1991-12-23
Handbook Of Polymer Synthesis written by Hans R. Kricheldorf and has been published by CRC Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 1991-12-23 with Technology & Engineering categories.
A compact but comprehensive review of the most important preparative methods for the synthesis and chemical modification of polymers. The contents of the two-volume handbook (Part A was cited in the May 1992 SciTech Book News) are subdivided according to the chemical structure of the polymer backbone on the one hand (Chapters 1-14 of Part A and 15-18 of Part B) and special properties and applications of polymers regardless of their chemical structure on the other hand (Chapters 19-27 of Part B). The latter chapters deal with, for instance, electroconductive polymers, polymeric reagents, and models of bio-polymers. Includes some 11,000 references to the original literature. Annotation c. by Book News, Inc., Portland, Or.