Dendrimers characterization

The earliest work on dendrimer characterization was concerned with aspects of the organic chemistry - did the proposed chemical reaction take place without side reactions and what was the conversion Since near-100% conversion and near-perfect removal of excess reactants is required for making pure dendrimer, common methods of spectroscopy and chromatography can be used to verify the structure. In a wide variety of dendrimer chemistries, nearly perfect structures have been produced, at least for earlier generations wherein the techniques are more quantitative. 

Dendrimer characterization was accomplished by 13C, NMR and FT-IR spectroscopy as well as mass spectrometry using fast atom bombardment (FAB) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) techniques. Molecular ion base peaks were observed in the MALDI-TOF MS of polyester 168 (mlz 18900 (calcd. 19044)) along with minor peaks at 37000 and 54000 mlz corresponding to ionic gasphase dimer and trimer complexes. 

Finally, the 64-branch phosphine DAB-t e r-G4-[N(CH2PPh2)2]32 analogously reacts with [Ru3(CO)i2] and 1 % [Fe Cp( -C6Me6)] (20°C, THF, 20 min) to give the dark-red 192-Ru dendrimer. Characterization of the purity of these dendrimer-cluster assemblies is conveniently monitored by P NMR. This application should find extension to other metal-carbonyl clusters and other families of phosphine dendrimers. 

Standards commonly employed [5] to calibrate SEC columns do not have a well-defined size. Carefully characterized spherical solutes in the appropriate size range are therefore of considerable interest. The chromatographic behavior of carboxylated starburst dendrimers — characterized by quasi-elastic light scatter-... 

Liquid crystalline dendrimers characterized by a well-defined molecular weight and exhibiting thermotropic columnar mesophases have been reported very recently. An example is the dendrimers based on the stiff, triconnected phenylacetylene monomer [93] is shown in Fig. 18. 

The possibility of using the thermotropic properties of macromolecular complexes of dendrimers was demonstrated by the example of oxidation of disulfides in the presence of a macromolecular complex of cobalt phthalocyanine with a polyisopropylacrylamide-based (PIPAAm-based) dendrimer characterized by temperature-dependent solubility. The oxidation rate is almost tripled by increasing the temperature from 34 to 36 °C [129]. These temperatures are close to... 

Several other techniques have been used for dendrimer characterization. However, information about the presence of cationic fragments is not as direct as the methods described above. Within this section, they will be briefly mentioned. 

X-ray scattering techniques are used to elucidate the crystal stmetures of solid materials. However, due to the high branching and mostly amorphous nature of dendrimers, the majority of the dendritic stmetures do not exhibit the required long-range order. Consequently, X-ray tedmiques have foimd only limited applicability for dendrimer characterization. 

A survey of the various analytical techniques used for the characterization of dendrimer was published by Caminade et al of these, NMR is certainly among the most valuable methods. The invaluable nature of NMR as a tool in the characterization of dendrimer is even more evident during the synthesis stage. NMR is able to provide information on the reactions at the end groups during each step thus serving as a tool to prove success at each step in the synthetic procedure. Other aspects of dendrimer characterization which are important and yet not routinely studied are the molecular conformation and shape. 

AB2 reacts selectively with only one antagonist function of a second polyfunctional molecule, the other ones being protected81 (Fig. 5.16). The perfect hyperbranched molecules obtained according to that step-by-step process are called dendrimers. The degree of branching characterizes the structure of a hyperbranched polymer and has been defined by Hawker et al.82 as... 

The data presented in Figure 8 graphically illustrate the tremendous and rapid growth in interest in FOSS chemistry, especially for patented applications. This looks set to continue with current applications in areas as diverse as dendrimers, composite materials, polymers, optical materials, liquid crystal materials, atom scavengers, and cosmetics, and, no doubt, many new areas to come. These many applications derive from the symmetrical nature of the FOSS cores which comprise relatively rigid, near-tetrahedral vertices connected by more flexible siloxane bonds. The compounds are usually thermally and chemically stable and can be modified by conventional synthetic methods and are amenable to the usual characterization techniques. The recent commercial availability of a wide range of simple monomers on a multigram scale will help to advance research in the area more rapidly. 

Dendrimers have been characterized by a variety of general techniques of analytical chemistry, and also by some specialized techniques that are particularly suitable for dendrimers. The following sections describe these techniques as they have been applied to dendrimers. For more details, the reader is referred to the books fisted in Further Reading section. 

Mass spectroscopy is a useful technique for the characterization of dendrimers because it can be used to determine relative molar mass. Also, from the fragmentation pattern, the details of the monomer assembly in the branches can be confirmed. A variety of mass spectroscopic techniques have been used for this, including electron impact, fast atom bombardment and matrix-assisted laser desorption ionization (MALDI) mass spectroscopy. 

Atomic force microscopy (AFM) has been used to characterize dendrimers that have been adsorbed onto a surface such as silica. AFM involves moving a finely tipped stylus across a surface and monitoring the tip movements as it traces the surface topography. In studying adsorbed dendrimers, samples can be scanned repeatedly and in a variety of directions. When this is done, it is found that all the images are the same. True dendrimers form objects of only one size. 

Cornils B (1999) Modern Solvent Systems in Industrial Homogeneous Catalysis.206 133-152 Crooks RM, Lemon III BI, Yeung LK, Zhao M (2001) Dendrimer-Encapsulated Metals and Semiconductors Synthesis, Characterization, and Applications. 212 81 -135 Croteau R, see Davis EM (2000) 209 53 - 95 CurranDP, see Maul JJ (1999) 206 79-105... 

An important goal of this study is to characterize the noncentrosymmetric arrangement of the azobenzene branches in dendrimers and the effect of these dendrimers on macroscopic second-order susceptibihty. The NLO activity of the dendrimers can be characterized by their molecular hyperpolarizabihty. The hyper-Rayleigh scattering (HRS) method is a reliable way of measuring the mol-... 

One of the main applications of dendrimers is in catalysis allowing easy recycling of the homogeneous catalyst by means of nanofiltration. Carbosilane dendrimers functionalized with diphenylphosphine groups at the periphery have been synthesized and characterized. Palladium complexes of these dendrimers have been used as catalysts in the allylic alkylation reaction. These dendrimeric catalysts can be used in a continuous process using a membrane reactor.509... 

---