Dendron Generation Research Articles

Leaching of Copper from Furnace Dust by Pure and Mixed Culture of Thiobacillus ferrooxidans and Thiobacillus thiooxidans

The synthesis of well-defined dendrons based on aliphatic polyether dendritic cores and glassy polystyrene peripheries is described. The synthetic route involves a combination of living anionic polymerization and a stepwise convergent method consisting of iterative Williamson etherification and hydroboration/oxidation reactions. On the basis of molecular weight, as characterized by gel permeation chromatography (GPC), the first generation dendron (Generation-1) shows a random coil conformation like a linear polystyrene, while higher generations (Generation-2 and 3) reveal globular forms in solution.

Synthesis and Characterization of Aliphatic Polyether Dendrons Based on Polystyrene Peripheries

The synthesis of well-defined dendrons based on aliphatic polyether dendritic cores and glassy polystyrene peripheries is described. The synthetic route involves a combination of living anionic polymerization and a stepwise convergent method consisting of iterative Williamson etherification and hydroboration/oxidation reactions. On the basis of molecular weight, as characterized by gel permeation chromatography (GPC), the first generation dendron (Generation-1) shows a random coil conformation like a linear polystyrene, while higher generations (Generation-2 and 3) reveal globular forms in solution.

Interaction between Dendrons Directly Studied by Single-Molecule Force Spectroscopy

In this article, we have investigated the interaction between two poly(benzyl ether) dendrons directly by single-molecule force spectroscopy. For this purpose, one dendron was immobilized on an AFM tip through a poly(ethylene glycol) (PEG) spacer, and the other dendron was anchored on a gold substrate as a self-assembled monolayer. Two dendrons approached and then interacted with each other when the AFM tip and the substrate moved close together. The rupture force between dendrons was measured while the AFM tip and the substrate separated. PEG as a flexible spacer can function as a length window for recognizing the force signals and avoiding the disturbance of the interaction between the AFM tip and the substrate. The interaction between two first-generation dendrons is measured to be about 224 pN at a force loading rate of 40 nN/s. The interaction between second- and first-generation dendrons rises to 315 pN at the same loading rate. Such interactions depend on the force loading rate in the range of several to hundreds of nanonewtons per second, indicating that the rupture between dendrons is a dynamic process. The study of the interaction between surface-bound dendrons of different generations provides a model system for understanding the surface adhesion of molecules with multiple branches. In addition, this multiple-branch molecule may be used to mimic the sticky feet of geckos as a man-made adhesive.

Synthesis and characterization of processible polyaniline containing plasticizing dendron-type dopants

Bifunctional dendrons consisting of sulfonic acid core and plasticizing peripheral groups were synthesized and used for polyaniline doping. The second generation dendrons were prepared in a two step procedure involving esterification of iminodiacetic acid, followed by the reaction of the resulting diester with sulfosuccinic acid. Plasticizing dendrons facilitate polyaniline solution processing and efficiently protonate it, despite their relatively large size (molar mass from 764 to 1100 g/mol). Their size and shape influence however the supramolecular organization of the polyaniline–dopant associations. Layered structure, clearly seen in for polyaniline protonated with first generation dendrons by X-ray diffraction, is lost for polyaniline protonated with the second generation ones. The polymer retains its film forming properties giving by casting from dichloroacetic acid solution free standing films which combine plasticized state with reasonably good conductivity from 1 to 8.5 S/cm.

Synthesis and Properties of Carborane-Containing Dendronized Polymers

Carborane-containing dendronized polymers were successfully synthesized using two different approaches up to the fourth generation. Nitroxide-mediated polymerization (NMP) was effective for the polymerization of carborane-functionalized styrenic monomers, leading to well-defined polymers with high boron content and narrow molecular weight distributions (PDI < 1.1). The resulting carborane-functionalized polymers could then be dendronized using a divergent approach to introduce aliphatic polyester dendrons of generation 1−4 grafted from the polymer backbone. This first approach afforded a maximum degree of dendronization of 70%. To increase the degree of dendronization, a first-generation macromonomer was polymerized using NMP to yield a fully functionalized first-generation dendronized polymer. This material was also dendronized up to the fourth generation. Both approaches produced water-soluble dendronized polymers (1 mg/mL in pure water) with high molecular weights (in excess of 70 kDa). It was found that the solubility of the polymer produced from the second approach, where dendronization occurred at every monomer unit, exceeded that of the first approach.

Hydrodynamic and conformational properties of poly(acrylate) molecules with side dendrons based on L-aspartic acid

The conformational properties of poly(acrylate) with L-aspartic acid-based side dendrons of the first and second generations with hexyloxycarbonyl end groups have been studied by the methods of molecular hydrodynamics. Regularly branched dendrons are separated from the main chain by a benzamide fragment. The degree of polymerization of the main chain varies within 30-and 50-fold intervals for the dendrons of first and second generations, respectively. Mark-Kuhn-Houwink equations have been derived for poly(acrylate) in bromoform and dichloroacetic acid containing lithium chloride additives. The experimental results are discussed in terms of the models of the wormlike chain, weakly bent cylinder, and solid ellipsoid of revolution. On the basis of translational and rotational friction data, the persistent length of poly(acrylate) in bromoform and dichloroacetic acid containing small amounts of lithium chloride has been estimated.

Self-assembly and supramolecular transition of poly(amidoamine) dendrons focally modified with aromatic chromophores

Three novel series of amphiphiles based on poly(amidoamine) dendrons (from G1 to G3) and having different aromatic chromophores (Cz I, Cz II, and Py) at the focal point were synthesized and studied for their self-assembly behavior in aqueous solution by using electronic microscopies (i.e., SEM and TEM), UV–vis, fluorescence, IR, and 1H NMR spectroscopy. It was found that the generation of dendrons affected significantly the self-assembly of these amphiphiles in aqueous solution and the morphological structures of the resulting assemblies depended greatly on the architecture of the focal chromophores. As a result, the first generation of dendrons assembled readily into vesicles at low concentrations. These vesicular structures subsequently fused to form a stable tubular structure. Similar tubular structures could also be directly obtained through self-assembly of these amphiphilic dendrons at high concentrations. X-ray investigations showed that the resulting tubules possessed a lamellar structure. A head-to-head packing model of amphiphilic dendrons in the assemblies was proposed.

Synthesis and opto‐electrical properties of dendron‐containing poly(2,3‐diphenyl‐1,4‐phenylenevinylene) derivatives

AbstractA new series of poly(2,3‐diphenyl‐1,4‐phenylenevinylene) derivatives containing dendritic side groups were synthesized. Different generations of dendrons were integrated on the pendant phenyl ring to investigate their effect on optical and electrical properties of final polymers. Homopolymers can not be obtained via the Gilch polymerization because of sterically bulky dendrons. By controlling the feed ratio of different monomers during polymerization, dendron‐containing copolymers with high molecular weights were obtained. The UV–vis absorption and photoluminescent spectra of the thin films are pretty close; however, quantum efficiency is significantly enhanced with increasing the generation of dendrons. The electrochemical analysis reveals that hole‐injection is also improved by increasing dendritic generation. Double‐layer light‐emitting devices with the configuration of ITO/PEDOT:PSS/polymer/Ca/Al were fabricated. High generation dendrons bring benefit of improved device performance. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3440–3450, 2007

Organo-clay hybrids based on dendritic molecules: preparation and characterization

Three generations of dendrons (G1, G2 and G3) with phenyl end-groups wereintercalated into montmorillonite (MMT) layered silicates in dimethylformamide/watercosolvent. These dendrons synthesized via the convergent route weredifferent in size and shape with molecular weights ranging from 930 to5975 g mol−1. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM)indicate that the respective intercalations of MMT with G1, G2 and G3 dendrons exhibitedorganized characteristics, and the interlayer spacings were 38, 77 and 115 Å for G1/MMT,G2/MMT and G3/MMT, respectively. Furthermore, the modified dendron/MMT hybridscould be well dispersed into organic solvents, such as DMF, due to the presence ofhydrophobic dendritic molecules. Our results indicate that organic/inorganic hybridsresulting from the association of dendrons and inorganic layered silicate can be obtainednot only by ionic exchange reaction, but possibly by a direct organized route as well.Moreover, the preparation of dendron/MMT hybrids was investigated at differentdendron/MMT molar ratios regarding the changes of interlayer distance. When the molarratio is within the range of 0.25–1.0 cationic exchange capacity (CEC) equivalents, thed spacings increase from 19 to 38 Å for G1/MMT, 15 to 77 Å for G2/MMT and 14 to 115 Å forG3/MMT, revealing a conformation change of the intercalating dendrons.

Hydrogen‐Bonded Dendronized Polymers and Their Self‐Assembly in Solution

Frechet-type benzyl ether dendrons of second and third generations with a carboxyl group (G2, G3) at the apex site could attach to poly(4-vinylpyridine) (PVP), forming hydrogen-bonded dendronized polymers (HB denpols) in their common solvent, chloroform. The HB denpols show unique self-assembly behavior, forming vesicles in the common solvent under ultrasonic treatment. The structure and morphology of the vesicles were characterized by dynamic light scattering (DLS), static light scattering (SLS), SEM, TEM, and AFM. The size of the vesicles decreases and the thickness of the vascular membrane increases as the molar ratio of Gx/PVP increases. The hydrogen bonding, pi-pi aromatic stacking of the dendrons, and the considerable difference in architecture between the dendron Gx and PVP are the main factors facilitating the assembly of the HB denpols in the common solvent.

Supramolecular Dendrimers Self‐Assembled from Dendritic Fullerene Ligands and a Homotritopic Hamilton Receptor

AbstractSupramolecular dendrimers resulting from the self‐assembly of a series of dendrofullerens 2a–4b containing a cyanuric acid building block at their focal point with the homotritopic Hamilton receptor 1 were prepared. The 1:3 compositions of the supramolecular dendrimers as well as the association constants Kn and the cooperativity of binding expressed by Scatchard plots and Hill coefficients nH were determined by NMR titration experiments. The most pronounced positive cooperativity was observed for the 1:L3 complexes with L being first generation dendrons. With the bulky second generation dendrons less stable complexes are formed.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

Synthesis of Symmetrical and Unsymmetrical PAMAM Dendrimers by Fusion between Azide- and Alkyne-Functionalized PAMAM Dendrons

A new convergent synthetic method for the synthesis of PAMAM dendrimers has been developed. The fusion between propargyl-functionalized PAMAM dendrons and azido-functionalized PAMAM dendrons via the Cu(I)-catalyzed Huisgen [2 + 3] dipolar cycloaddition reaction (click chemistry) of an alkyne and an azide leads to the formation of symmetric PAMAM dendrimers in high yields. Furthermore, the coupling reactions between the different generation dendrons afford the size-differentiated unsymmetrical PAMAM dendrimers.

Solution processable phosphorescent rhenium(i) dendrimers

A family of (1,10-phenanthroline)rhenium(I)(CO)3Cl complex cored first generation dendrimers with one, two or three dendrons have been prepared. The first generation dendrons attached to the core complex are comprised of biphenyl units with 2-ethylhexyloxy surface groups at their distal ends. The number and position of attachment of the dendron to the core was found to have an effect on the properties of the dendrimers. When dendrons were attached to both the 2- and 9-positions of the 1,10-phenanthroline ligand, thus straddling the rhenium(I), the dendrimers became more electrochemically stable and less susceptible to solvatochromism. The dendrimers were generally found to have their emission blue-shifted and a higher photoluminescence quantum yield in the solid state than in the solution. The origin of this rigidochromism effect is discussed. A single layer device with a neat dendrimer film was found to have an external quantum efficiency of 0.4% (0.8 cd A−1) and power efficiency of 0.2 lm W−1 at 100 cd m−2 and 12.8 V.

Preparation of Multiallylic Dendronized Polymers via Anionic Polymerization

The anionic polymerization technique was investigated to prepare dendronized polymers (denpols) made of a polystyrene backbone and carbosilane dendrons. The monomers, namely 3,5-bis(3-triallylsilanylpropyloxy)styrene (G1-bis) and 3,4,5-tris(3-triallylsilanylpropyloxy) styrene (G1-tris), are fitted with respectively two or three allyl-terminated carbosilane dendrons of first generation. Polymers with monomodal molecular weight distribution and low polydispersity have been produced. Steric effects brought by the dendrons result in a slow polymerization rate, leading to an apparent saturation of the degree of polymerization. As a matter of fact, polymers of highest molecular weight could only be obtained from the less bulky monomer G1-bis. When the polymerization is complete or drastically reduced by steric factors, an intramolecular transfer reaction is suspected to take place. Finally, the solubility and thermal properties of these multiallylic denpols are discussed.

Steric Communication of Chiral Information Observed in Dendronized Polyacetylenes

Structural and retrostructural analysis of helical dendronized polyacetylenes (i.e., self-organizable polyacetylenes containing first generation dendrons or minidendrons as side groups) synthesized by the polymerization of minidendritic acetylenes with [Rh(nbd)Cl]2 (nbd = 2,5-norbornadiene) reveals an approximately 10% change in the average column stratum thickness (l) of the cylindrical macromolecules with a chiral periphery, through which a strong preference for a single-handed screw-sense is communicated. The cylindrical macromolecules reversibly interconvert between a three-dimensional (3D) centered rectangular lattice (Phi r-c,k) exhibiting long-range intracolumnar helical order at lower temperatures and a two-dimensional (2D) hexagonal columnar lattice (Phi h) with short-range helical order at higher temperatures. A polymer containing chiral, nonracemic peripheral alkyl tails is found to have a larger l as compared to the achiral polymers. In methyl cyclohexane solution, the same polymer exhibits an intense signal in circular dichroism (CD) spectra, whose intensity decreases upon heating. The observed change in l indicates that the chiral tails alter the polymer conformation from that of the corresponding polymer with achiral side chains. This change in conformation results in a relatively large free energy difference (DeltaGh) favoring one helix-sense over the other (per monomer residue). The capacity to distort the polymer conformation and corresponding free energy is related to the population of branches in the chiral tails and their distance from the polymer backbone by comparison to recently reported first and second generation dendronized polyphenylacetylenes.

Synthesis and characterization of poly(fluorene‐co‐alt‐phenylene) containing 1,3,4‐oxadiazole dendritic pendants

AbstractA series of poly(fluorene‐co‐alt‐phenylene)s containing various generations of dendritic oxadiazole (OXD) pendent wedges were synthesized by the Suzuki polycondensation of OXD‐functionalized 1,4‐dibromophenylene with 9,9‐dihexylfluorene‐2,7‐diboronic ester. The obtained polymers possessed excellent solubility in common solvents and good thermal stability. Photophysical studies showed that the dendronized polymers appended with higher generations of OXD dendrons exhibited enhanced photoluminescence efficiencies and narrower values of the full width at half‐maximum. This was attributed to the shielding effect induced by the bulky dendritic OXD side chains, which prevented self‐quenching and suppressed the formation of aggregates/excimers. The energy transfer from the OXD dendrons to the polymer backbones was very efficient when excitation of the peripheral OXD dendrons resulted mainly in the polymer backbone emission alone. In particular, the photoluminescence emission intensities by the sensitized excitations of OXD dendrons in solid films of the polymers were all stronger than those by the direct excitations of their polymer conjugated backbones. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6765–6774, 2006

Synthesis and MALDI‐TOF analysis of dendritic‐linear block copolymers of lactides: Influence of architecture on stereocomplexation

AbstractFormation of a stereocomplex from polylactide copolymers can be tuned by changing the size and the chain topology of the second block in the copolymer. In particular, the use of a dendritic instead of linear architecture is expected to destabilize the cocrystallisation of polylactide blocks. With this idea in mind, dendritic‐linear block copolymers were synthesized by ring‐opening polymerization (ROP) of lactides using benzyl alcohol dendrons of generation 1–3 as macroinitiators and stannous octoate as catalyst. Polymers with controlled and narrow molar mass distribution were obtained. The MALDI‐TOF mass spectra of these dendritic‐linear block copolymers show well‐resolved signals. Remarkably, 10% or less of odd‐membered polymers are present, indicating that ester‐exchange reactions which occur classically parallel to the polymerization process, were in these conditions, very limited. Thermal analysis of polyenantiomers of generation 1–3 and the corresponding blends were examined. The blend of a pair of enantiomeric dendritic‐linear block copolymers exhibit a higher melting temperature than each copolymer, characteristic for the formation of a stereocomplex. Melting temperatures are strongly dependent on the dendron generation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6782–6789, 2006

Formation of CdS Nanoparticle Necklaces with Functionalized Dendronized Polymers

A one-dimensional assembly of cadmium sulfide (CdS) nanoparticles was prepared by using functionalized polymers with pendant Fréchet-type dendritic wedges of different generation. The novel dendronized polymers acted as both nanoreactors for the formation of CdS nanoparticles and a template to arrange the nanoparticles into a necklace. The polymers of different dendron generation were applied to stabilize CdS particles and the effect of dendron size was observed. CdS nanoparticle necklaces were obtained successfully when polymers bearing second-generation dendrons were applied.

Cover Picture: Exploring and Expanding the Structural Diversity of Self‐Assembling Dendrons through Combinations of AB, Constitutional Isomeric AB2, and AB3 Biphenyl‐4‐Methyl Ether Building Blocks (Chem. Eur. J. 24/2006)

Seven libraries with up to three generations of amphiphilic dendrons based on AB, constitutional isomeric AB2, and AB3 biphenyl‐4‐methyl ether building blocks were synthesized by Percec et al., as described on page 6216ff., and analyzed by using the retrostructural analysis method shown. These dendrons self‐assemble into hollow and non‐hollow supramolecular dendrimers up to twice as large as those for the architecturally related benzyl ether. These results expand the structural diversity of non‐hollow and hollow supramolecular dendrimers and demonstrate the generality of self‐assembling dendrons based on amphiphilic arylmethyl ethers.

DFT analysis of structure and IR spectra of phosphorus G1 v generation dendron

FT-IR spectra of phosphorus dendron G 1 v generation with terminal P-Cl groups have been recorded. Density functional theory is used for analyzing the properties of each structural part (core, branches, surface). It is found that the repeating branching units of G 1 v exist in a single stable conformation with planar -O C 6H 4 CH N N(CH 3)-P fragments. DFT results for the structure of G 1 v are in good agreement with recent X-ray diffraction measurements. A complete vibrational assignment is proposed for different parts of G 1 v . The global and local reactivity descriptors have been used to characterize the reactivity pattern of the core function and terminal group. Our study reveals that the most reactive site of G 1 v is the core function and =CH 2 side of vinyl group is preferred for nucleophilic attack. In the dendrimer G 1 the most reactive are the terminal groups. IR spectroscopy combined with ab initio DFT computation provides unique detailed information about the structure and reactivity of the technologically relevant materials, which could not be obtained before with any other technique.