Dendrimers in Supramolecular Chemistry: From Molecular Recognition to Self-Assembly.

1. Multifunctional Initiators. 3749 2. Multifunctional Linking Agents 3751 3. Use of Difunctional Monomers 3754 B. Star−Block Copolymers 3754 C. Functionalized Stars 3755 1. Functionalized Initiators 3755 2. Functionalized Terminating Agents 3756 D. Asymmetric Stars 3757 1. Molecular Weight Asymmetry 3757 2. Functional Group Asymmetry 3760 3. Topological Asymmetry 3761 E. Miktoarm Star Polymers 3761 1. Chlorosilane Method 3761 2. Divinylbenzene Method 3766 3. Diphenylethylene Derivative Method 3766 4. Synthesis of Miktoarm Stars by Other Methods 3770

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Polymers with Complex Architecture by Living Anionic Polymerization

http://static.sif.it/SIF/resources/public/files/va2012/likos_0710.pdf

Effective interactions in soft condensed matter physics

“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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Hyperbranched and highly branched polymer architectures--synthetic strategies and major characterization aspects.

In the last 12 years the field of hyperbranched polymers has been well established with a large variety of synthetic approaches and fundamental studies on structure and properties of these unique materials. However, new developments involving hyperbranched materials appeared recently, for example, different synthetic strategies, new reaction mechanisms, formation of more complex architectures, a deeper understanding of the branched structure and their kinetic development, and intensive studies on the material properties and possible applications. This demonstrates the high versatility and the possibilities that are still involved in hyperbranched polymers and render it one of the most active fields in polymer science with a very promising future. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2505–2525, 2000

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1099-0518%2820000715%2938%3A14%3C2505%3A%3AAID-POLA10%3E3.0.CO%3B2-8

New developments in hyperbranched polymers

Carbosilane dendrimers with 64 and 128 surface Si-Cl bonds were used as coupling reagents for monodisperse poly(butadienyl)lithium. Two series of regular star polybutadienes with 64 and 128 arms were prepared. The arm molecular weight was varied between 6400 and 72 000. The dilute-solution properties of the stars were determined in a good solvent (cyclohexane) and in a θ-solvent (dioxane) for polybutadiene. Measurements of R G . A 2 , D 0 , and [η] indicate that the isolated stars behave as hard spheres. The ratio of the hydrodynamic radius over the radius of gyration is slightly larger than (5/3) 1/2

Regular star polymers with 64 and 128 arms. Models for polymeric micelles

A series of carbosilane dendritic macromolecules grown from four directions of a tetrahedral central core has been synthesized and characterized. In the synthesis tetravinylsilane is used as the central core molecule and dichloromethylsilane as the propagation unit. Two reactions are involved in the synthesis of each generation: hydrosilylation of vinylsilane with dichloromethylsilane and nucleophilic replacement of silicon chloride by vinylmagnesium bromide. The reaction conditions for hydrosilylation must be well controlled.

Synthesis of novel carbosilane dendritic macromolecules

Using small angle neutron scattering, the authors investigated the conformation of star polymers with functionalities ranging from f = 8 to f = 128 in a good solvent. The stars were made anionic polymerization of isoprene or butadiene using multifunctional chlorosilane linking agents. Single star form factors at zero concentration were determined by extrapolating low concentration data to [phi] = 0. Conformations at finite concentrations were obtained by the zero average contrast method. In general the star form factors are well described in terms of the Daoud-Cotton scaling model. This concerns the molecular weight, functionality, and concentration dependence of R[sub G] as well as the shape of the form factor. In particular the step height between the low Q and asymptotic power law regime was found to follow an f[sup 3/2] law. Furthermore, with increasing functionality the star form factors were found to tend toward spherelike behavior, bearing evidence for a secondary maximum at the position of the third oscillation of the corresponding sphere form factor.

Lin Lin Zhou

Papers

Regular star polymers with 64 and 128 arms. Models for polymeric micelles

Synthesis of novel carbosilane dendritic macromolecules

Structural investigation of star polymers in solution by small angle neutron scattering