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

Cylindrical molecular brushes: Synthesis, characterization, and properties

“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.

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

The static and kinetic aspects of the order-disorder transition (ODT) in newly synthesized model 3-miktoarm star copolymer (simple graft) of SI2 type, (polystyrene)(polyisoprene) 2 , and a 3-miktoarm star terpolymer of SIB type, (polystyrene)(polyisoprene)(polybutadiene), have been studied using SAXS and rheology. The morphology and the order-disorder transition temperature (T ODT ) have been identified from the two-dimensional SAXS patterns with shear-oriented samples. Hexagonally ordered cylindrical microdomains aligned along the direction of shear and with T ODT =379 K have been formed for both samples studied. The SAXS profiles at temperatures well above the T ODT have been fitted to the mean-field theory (MFT) for graft copolymers. Near the ODT deviations from the theory have been observed and the SAXS data provide unambiguous evidence for the existence of fluctuations. The T ODT obtained from rheology is in excellent agreement with the one from SAXS. Discontinuities in the SAXS peak intensity and in the storage modulus near the T ODT are more pronounced in these systems as compared to linear diblocks. The ordering kinetics have been studied with rheology and complementary with SAXS. The width of the kinetically accessible metastable region is enlarged as compared to linear diblocks. For shallow quenches the ordering proceeds by heterogeneous nucleation and growth of three-dimensional grains with cylindrical microstructure. Our kinetic studies probe the metastable states near but below the T ODT

Microphase separation in model 3-miktoarm star copolymers (simple graft) and terpolymers .1. statics and kinetics

The method of Iatrou et al. (Macromolecules 1998, 31, 6697) was applied to synthesize a normal comb polystyrene sample with uniform side chains equally spaced along the main chain but with the most probable distribution in the main chain length. The molecular weights of the side chain and the connector (the part of the main chain between the neighboring side chains) were 3.5 × 104 and 2.3 × 104, respectively. The sample was analyzed using a gel-permeation chromatography system with a multiangle light scattering and refractive index detector to determine the relationship between the z-average mean square radius of gyration 〈S2〉 and the weight-average molecular weight Mw. Tetrahydrofuran (THF) was chosen as the solvent. The relation fell considerably below that for linear polystyrene. The slope of the plot of log 〈S2〉1/2 vs log Mw for the comb polymer was 0.46, a value much smaller than the Flory exponent 0.6 for linear chains in good solvents. Similar measurements were also made on polystyrene centipedes p...

Radius of gyration of polystyrene combs and centipedes in solution (vol 33, pg 8323, 2000)

The hierarchical self-assembly at the submicrometer, nanometer and α-helical length scales has been studied in a miktoarm star rod−coil chimera composed of poly(γ-benzyl-l-glutamate) (PBLG), polystyrene, and polyisoprene blocks by X-ray scattering, solid state NMR, and transmission electron microscopy. The propensity of the rod block toward α-helices that are further hexagonally packed gives rise to pure PBLG domains and induces the partial mixing of the two amorphous blocks. These structural results were confirmed by independent dynamic probes at the segmental and α-helical level by NMR and dielectric spectroscopy, respectively.

Hierarchical Self-Assembly and Dynamics of a Miktoarm Star chimera Composed of Poly(gamma-benzyl-L-glutamate), Polystyrene, and Polyisoprene

Anionic polymerization high vacuum techniques have proven to be a very powerful tool for the synthesis of well-defined macromolecules with complex architectures. Until now, however only a relatively limited number of such structures with two or thee different components (star block, miktoarm star, graft, branched, cyclic, hyperbranched) have been created, the potential of anionic polymerization is unlimited. Imagination, nature, and other scientific disciplines (i.e., polymer physics, materials science, and molecular biology) will lead polymer scientists to novel structures, with the ultimate goal of designing and synthesizing polymeric materials with predetermined properties. A short review of the structure/property relationships and applications of selected polymers will be presented.

H. Iatrou

Papers

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

Microphase separation in model 3-miktoarm star copolymers (simple graft) and terpolymers .1. statics and kinetics

Radius of gyration of polystyrene combs and centipedes in solution (vol 33, pg 8323, 2000)

Hierarchical Self-Assembly and Dynamics of a Miktoarm Star chimera Composed of Poly(gamma-benzyl-L-glutamate), Polystyrene, and Polyisoprene

Well-Defined Complex Macromolecular Architectures by Anionic Polymerization High Vacuum Techniques: Synthesis, Properties and Applications