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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 (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.
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.
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.
This comprehensive, truly one-stop reference discusses monomers, methods, stereochemistry, industrial applications and more. Chapters written by internationally acclaimed experts in their respective fields cover both basic principles and up-to-date information, ranging from the controlled ring-opening polymerization methods to polymer materials of industrial interest. All main classes of monomers including heterocyclics, cyclic olefins and alkynes, and cycloalkanes, are discussed separately as well as their specificities regarding the ring-opening polymerization techniques, the mechanisms, the degree of control, the properties of the related polymers and their applications. The two last chapters are devoted to the implementation of green chemistry in ring-opening polymerization processes. Of much interest to chemists in academia and industry.
Edited by a leading authority in the field, the first book on this important and emerging topic provides an overview of the latest trends in sequence-controlled polymers. Following a brief introduction, the book goes on to discuss various synthetic approaches to sequence-controlled polymers, including template polymerization, genetic engineering and solid-phase chemistry. Moreover, monomer sequence regulation in classical polymerization techniques such as step-growth polymerization, living ionic polymerizations and controlled radical polymerizations are explained, before concluding with a look at the future for sequence-controlled polymers. With its unique coverage of this interdisciplinary field, the text will prove invaluable to polymer and environmental chemists, as well as biochemists and bioengineers.
It is generally accepted that a new material is often developed by ?nding a new synthesis method of reaction or a new reaction catalyst. Historically, a typical example may be referred to as a Ziegler–Natta catalyst, which has allowed large-scale production of petroleum-based polyole?ns since the middle of the 20th century. New polymer synthesis, therefore, will hopefully lead to creation of new polymer materials in the 21st century. This special issue contributed by three groups focuses on recent advances in polymer synthesis methods, which handle the cutting-edge aspects of the advanced technology. The ?rst article by Yokozawa and coworkers contains an overview of the - action control in various condensation polymerizations (polycondensations). Advanced technologies enabled the control of stereochemistry (regio-, g- metrical-, and enantio-selections), chemoselectivity, chain topology, and st- chiometry of monomers, giving a high molecular weight polymer. It has been recognized for a long time, however, that polycondensation is a dif?cult p- cess in controlling the reaction pathway, because the reaction is of step-growth and the reactivity of monomers, oligomers, and polymers are almost the same during the reaction and hence, the molecular weight of polymers and its d- tribution (M /M ) are impossible to regulate. The authors’ group developed w n a new reaction system (chain-growth condensation polymerization), changing the nature of polycondensation from step-growth to chain-growth; namely the propagating chain-end is active, allowing for control of the product molecular weight as well as the distribution.
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.