Chain Walking: A New Strategy to Control Polymer Topology
26 Mar 1999-Science (American Association for the Advancement of Science)-Vol. 283, Iss: 5410, pp 2059-2062
TL;DR: Although the overall branching number and the distribution of short-chain branching change very slightly, the architecture or topology of the polyethylene changes from linearpolyethylene with moderate branches at high ethylene pressures to a hyperbranched polyethylenes at low pressures.
Abstract: Ethylene pressure has been used to control the competition between isomerization (chain walking) and monomer insertion processes for ethylene coordination polymerization catalyzed by a palladium-α-diimine catalyst. The topology of the polyethylene varies from linear with moderate branching to “hyperbranched” structures. Although the overall branching number and the distribution of short-chain branching change very slightly, the architecture or topology of the polyethylene changes from linear polyethylene with moderate branches at high ethylene pressures to a hyperbranched polyethylene at low pressures.
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TL;DR: A review of the catalytic activity of metal complexes of binaphthyl compounds and their combinations with salen Schiff base is presented in this paper, where the pyridyl bis (imide) and pyridine bis(imine) complexes of cobalt(II), iron(II) ions have been used as catalysts in the polymerization of ethylene and propylene.
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TL;DR: A review of the historical roles that quantized building blocks such as atoms and monomers have played in the development of small molecule and traditional polymer synthesis, respectively, is presented in this article, where the unique features of traditional macromolecular architectures (i.e. linear, crosslinked, branched), as well as controlled nanostructures in biology were used as frames of reference to anticipate potential new properties, phenomena and synthetic constructs that should be expected to emerge at the interface of the dendritic architectural state.
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TL;DR: The challenging synthesis of the dendrimers attracted especially scientists with a strong organic chemistry background and led to beautifully designed macromolecules, which allowed a deeper insight into the effect of branching and functionality.
Abstract: “Life is branched” was the motto of a special issue of Macromolecular Chemistry and Physics1 on “Branched Polymers”, indicating that branching is of similar importance in the world of synthetic macromolecules as it is in nature. The significance of branched macromolecules has evolved over the last 30 years from just being considered as a side reaction in polymerization or as a precursor step in the formation of networks. Important to this change in perception of branching was the concept of “polymer architectures”, which formed on new starand graft-branched structures in the 1980s and then in the early 1990s on dendrimers and dendritic polymers. Today, clearly, controlled branching is considered to be a major aspect in the design of macromolecules and functional material. Hyperbranched (hb) polymers are a special type of dendritic polymers and have as a common feature a very high branching density with the potential of branching in each repeating unit. They are usually prepared in a one-pot synthesis, which limits the control on molar mass and branching accuracy and leads to “heterogeneous” products with a distribution in molar mass and branching. This distinguishes hyperbranched polymers from perfectly branched and monodisperse dendrimers. In the last 20 years, both classes of dendritic polymers, dendrimers as well as hb polymers, have attracted major attention because of their interesting properties resulting from the branched architecture as well as the high number of functional groups.2 The challenging synthesis of the dendrimers attracted especially scientists with a strong organic chemistry background and led to beautifully designed macromolecules, which allowed a deeper insight into the effect of branching and functionality. Dendrimers have been considered as perfect “nano-objects” where one can control perfectly size and functionality, which is of high interest in nanotechnology and biomedicine. hb polymers, however, were considered from the beginning as products suitable for larger-scale application in typical polymer fields like coatings and resins, where a perfect structure is sacrificed for an easy and affordable synthetic route. Thus, the first structures that were reported paralleled the chemistry used for linear polymers like typical polycondensation for polyester synthesis. More recently, unconventional synthetic methods have been adopted also for hb polymers and related structures. Presently, a vast variety of highly branched structures have been realized and studied regarding their properties and potential application fields. Excellent reviews appeared covering synthesis strategies, properties, and applications, like the very recent tutorial by Carlmark et al.,3 the comprehensive book on hyperbranched polymers covering extensively synthesis and application * E-mail: voit@ipfdd.de; lederer@ipfdd.de. Chem. Rev. 2009, 109, 5924–5973 5924
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TL;DR: It is proposed that this entropically unfavorable process is offset by an enthalpy gain due to an increase in molecular contacts at dispersed nanoparticle surfaces as compared with the surfaces of phase-separated nanoparticles.
Abstract: Traditionally the dispersion of particles in polymeric materials has proven difficult and frequently results in phase separation and agglomeration. We show that thermodynamically stable dispersion of nanoparticles into a polymeric liquid is enhanced for systems where the radius of gyration of the linear polymer is greater than the radius of the nanoparticle. Dispersed nanoparticles swell the linear polymer chains, resulting in a polymer radius of gyration that grows with the nanoparticle volume fraction. It is proposed that this entropically unfavorable process is offset by an enthalpy gain due to an increase in molecular contacts at dispersed nanoparticle surfaces as compared with the surfaces of phase-separated nanoparticles. Even when the dispersed state is thermodynamically stable, it may be inaccessible unless the correct processing strategy is adopted, which is particularly important for the case of fullerene dispersion into linear polymers.
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References
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01 Jan 1981TL;DR: In this paper, the authors present an overview of the properties of polymers and their applications in the literature, including the following: 1.1 Types of Polymers and Polymerization. 2.3 Linear, Branched, and Crosslinked Polymers.
Abstract: Preface. 1. Introduction. 1.1 Types of Polymers and Polymerizations. 1.2 Nomenclature of Polymers. 1.3 Linear, Branched, and Crosslinked Polymers. 1.4 Molecular Weight. 1.5 Physical State. 1.6 Applications of Polymers. 2. Step Polymerization. 2.1 Reactivity of Functional Groups. 2.2 Kinetics of Step Polymerization. 2.3 Accessibility of Functional Groups. 2.4 Equilibrium Considerations. 2.5 Cyclization versus Linear Polymerization. 2.6 Molecular Weight Control in Linear Polymerization. 2.7 Molecular Weight Distribution in Linear Polymerization. 2.8 Process Condition. 2.9 Multichain Polymerization. 2.10 Crosslinking. 2.11 Molecular Weight Distributions in Nonlinear Polymerizations. 2.12 Crosslinking Technology. 2.13 Step Copolymerization. 2.14 High-Performance Polymers. 2.15 Inorganic and Organometallic Polymers. 2.16 Dendric (Highly Branched) Polymers. 3. Radical Chain Polymerization. 3.1 Nature and Radical Chain Polymerization. 3.2 Structural Arrangement of Monomer Units. 3.3 Rate of Radical Chain Polymerization. 3.4 Initiation. 3.5 Molecular Weight. 3.6 Chain Transfer. 3.7 Inhibition and Retardation. 3.8 Determination of Absolute Rate Constants. 3.9 Energetic Characteristics. 3.10 Autoacceleration. 3.11 Molecular Weight Distribution. 3.12 Effect of Pressure. 3.13 Process Conditions. 3.14 Specific Commercial Polymers. 3.15 Living Radical Polymerization. 3.16 Other Polymerizations. 4. Emulsion Polymerization. 4.1 Description of Process. 4.2 Quantitative Aspects. 4.3 Other Characteristics of Emulsion Polymerization. 5. Ionic Chain Polymerization. 5.1 Comparison of Radical and Ionic Polymerization. 5.2 Cationic Polymerization of the Carbon-Carbon Double Bond. 5.3 Anionic Polymerization of the Carbon-Carbon Double. 5.4 Block and Other Polymer Architecture. 5.5 Distinguishing Between Radical, Cationic, and Anionic Polymerizations. 5.6 Carbonyl Polymerization. 5.7 Miscellaneous Polymerizations. 6. Chain Copolymerization. 6.1 General Considerations. 6.2 Copolymer Composition. 6.3 Radical Copolymerization. 6.4 Ionic Copolymerization. 6.5 Deviations from Terminal Copolymerization Model. 6.6 Copolymerizations Involving Dienes. 6.7 Other Copolymerizations. 6.8 Applications of Copolymerizations. 7. Ring-Opening Polymerization. 7.1 General Characteristics. 7.2 Cyclic Ethers. 7.3 Lactams. 7.4 N-Carboxy-alphaAmino Acid Anhydrides. 7.5 Lactones. 7.6 Nitrogen Heterocyclics. 7.7 Sulfur Heterocyclics. 7.8 Cycloalkenes. 7.9 Miscellaneous Oxygen Heterocyclics. 7.10 Other Ring-Opening Polymerizations. 7.11 Inorganic and Partially Inorganic Polymers. 7.12 Copolymerization. 8. Stereochemistry of Polymerizaton. 8.1 Types of Stereoisomerism in Polymers. 8.2 Properties of Stereoregular Polymers. 8.3 Forces of Stereoregulation in Alkene Polymerization. 8.4 Traditional Ziegler-Natta Polymerization of Nonpolar Alkene Monomers. 8.5 Metallocene Polymerization of Nonpolar Alkene Monomers. 8.6 Other Hydrocarbon Monomers. 8.7 Copolymerization. 8.8 Postmetallocene: Chelate Initiators. 8.9 Living Polymerization. 8.10 Polymerization of 1,3-Dienes. 8.11 Commercial Applications. 8.12 Polymerization of Polar Vinyl Monomers. 8.13 Alehydes. 8.14 Optical Activity in Polymers. 8.15 Ring-Opening Polymerization. 8.16 Statistical Models of Propagation. 9. Reactions of Polymers. 9.1 Principles of Polymers Reactivity. 9.2 Crosslinking. 9.3 Reactions of Cellulose. 9.4 Reactions of Poly(vinyl) acetate). 9.5 Halogenation. 9.6 Aromatic Substitution. 9.7 Cyclization. 9.8 Other Reactions. 9.9 Graft Copolymers. 9.10 Block Copolymers. 9.11 Polymers as Carriers or Supports. 9.12 Polymer Reagents. 9.13 Polymer Catalysts. 9.14 Polymer Substrates. Index.
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