Hyperbranched materials

In summary, a wide variety of germanium-containing polymers has been synthesized. Most of the emphases has focused on the synthesis and characterization of the polygermanes. This emphasis will continue. Because of the cost and lack of ready availability of suitable germanimn monomers, research with germanium-containing polymers will continue to lag behind that of silicon- and tin-containing polymers. 

Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed., Wiley, New Ifork, 1988. 

Jurkschat, M. Mehring, in Organometallic Polymers of Germanium, Tin, and Lead. vol. 2, Z. Rappoport, ed., Wiley, New York, 2002. 

Lesbre, E Mazerolles, J. Satge, The Organic Compounds of Germanium, Wiley, New Y rk, 1971. 

in Comprehensive Organometallic Chemistry II, A. G. Davies, ed., Pergamon, Oxford, 1995. 

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The polymerization using sugar oxazoline monomers is not limited to the synthesis of linear aminopolysaccharides as described above and can be extended to formation of a hyperbranched material. Synthesis of hy-perbranched aminopolysaccharide was achieved by acid-catalyzed polymerization of a sugar oxazoline monomer, 8, having two hydroxy groups at position 3 and 4, which can be considered as an AB2 monomer (Scheme 9) [12]. This is the first example of the synthesis of a hyper-... 

These theoretical results are confirmed experimentally. In attempts to prepare a resin with a ratio of the starting materials of HHPA diisopropanolamine 2.3 1 the mixture gelated. This is reflected in Scheme 1, example 1 (n = 2). If a ratio of HHPA diisopropanolamine 3.2 1 is chosen (Scheme 1, example 2, n = 5/6), the system does not gelate. By GPC analysis it was verified that the theoretical assumptions made in Scheme 1 are valid for this system. Besides the hyperbranched material, the presence of hexahydrophthalic acid is demonstrated. The quantity of the acid is in close agreement (29 %) with the calculated value (28%). 

The successful application development for hyperbranched polyesteramides is primarily based on the many research programs started several years ago for dendrimers. For most of the potential and existing applications the high number of end groups and the multifunctionality are the predominant advantages. These characteristics are shared by dendrimers and hyperbranched materials alike. Only in some special cases, such as medical applications [23], is monodis-persity the main issue and thus dendrimers are preferred in this particular case. 

Reichert and Mathias prepared related branched aramids, to those of Kim,t5-34] from 3,5-dibromoaniline (23) under Pd-catalyzed carbonylation conditions (Scheme 6.7). These brominated hyperbranched materials (24) were insoluble in solvents such as DMF, DMAc, and NMP, in contrast to the polyamine and polycarboxylic acid terminated polymers that Kim synthesized, which were soluble. This supports the observation that surface functionality plays a major role in determining the physical properties of hyperbranched and dendritic macromolecules J4,36 A high degree of cross-linking could also significantly effect solubility. When a four-directional core was incorporated into the polymerization via tetrakis(4-iodophenyl)adamantanc,1371 the resultant hyperbranched polybromide (e.g., 25) possessed enhanced solubility in the above solvents, possibly as a result of the disruption of crystallinity and increased porosity. 

In 1993 during a visit to Bonn, we decided to document the early years of this dynamic topic, and Dendritic Molecules Concepts, Syntheses, Perspectives was conceived. The expansion of cascade construction into the macromolecular regime has in essence proven that there is no longer a molecular (weight or size) ceiling for chemists and others interested in materials science. We hope that this book will spark the reader s imagination to create new routes to dendritic or hyperbranched materials. In view of the increasing interest in macromolecular construction via dendrimers, there is little doubt in our minds that the surface of this topic has just been scratched. 

The actual formation of hyperbranched material proceeds during the polymerization of 3,5-difluoro-4 -hydroxydiphenyl sulfone in the presence of 3,4,5-trifluorophenylsulfonyl benzene or tris(3,4,5-trifluorophenyl)phos-phine oxide as a core molecule. Cyclic oUgomers formed dining this polymerization contribute to a low-molecular-weight polymer ranging from 3400 to 8400 Dalton. A triazin-based AB2 monomer has also been described. This monomer is shown in Figure 7.8. A hyperbranched aromatic poly(ether sulfone) with sulfonyl chloride terminal groups has been prepared by the polycondensation of 4,4 -(m-phenylenedioxy)-bis-(benz-enesulfonyl chloride). The polymerization was carried out in nitrobenzene at 120°C for 3 h in the presence of a catalytic amount of FeCls. ... 

The general area of dendritic and hyperbranched polymers has received remarkable attention over the past decade. New properties not available with linear polymers have been demonstrated. For example, evidence has been provided that supports the existence of considerable space for the encapsulation of small molecules, and this has led to the idea of a dendritic box" (69j. A severe problem with dendrimers is their timesynthetic methods that form hyperbranched materials that may exhibit many of the advantageous properties of dendritic macromolecules have been receiving significant attention (70j. 

Hyperbranched polymers can be prepared by a variety of techniques, including the polycondensation of AB monomers as originally described by Flory [113], the reaction of A2 + B3 monomers, and self-condensing vinyl polymerization [139-141]. The first report [142] of using click chemistry in the synthesis of hyperbranched materials appeared at about the same time as the initial report for dendrimers prepared using CuAAC however, but much fewer examples have been reported that describe hyperbranched materials involving click chemistry. Nevertheless, these polymers represent an important class of materials, and both CuAAC [142-147] and thiol-ene [148] chemistry have found their way into the hyperbranched hterature. 

Polymer Factory Sweden AB (PF) (http //www.polymerfaaory. com and subpages thereof, accessed 8 July 2010) is a manufacturer and provider of PBisMPA dendrons, dendrimers, and hyperbranched materials comprising a range of different end-group funaionalities and focal point moieties. The company has today the widest dendritic library available on the... 

A tremendous variety of hyperbranched materials have been synthesized (usually in one-pot reactions) via polycondensation of AB -type monomers, such as polyesters (via condensation... 

The polydisperse nature of hyperbranched materials would seem to make them ill-suited to the spontaneous self-assembly of precise structures. However, in 2004, Yan and coworkers demonstrated the assembly of hyperbranched materials into macroscopic objects. The structurally simple polymers were based on the known hyperbranched poly(3-ethyl-3-oxetanemelhanol) core (blue in 51, Figure 16), which was modified with oligo-ethyleneglycol arms. Stirring 51 in acetone, which is a... 

Hyperbranched materials and dendrimers — offer the synthetic ability to chemically tailor the branches in a step-wise fashion. 

Little has been reported on the formation of organogermanium dendrites and related hyperbranched products. Recently, Tang et al. described the synthesis of hyperbranched materials based on the diacetylene l,l-diethynyl-2,3,4,5-tetraphenyl-germole, 130. The homopolymerization of 130 to homopolymer 131 and and copolymerization with 1-octyne, 132, to copolymer 133 was accomplished (Scheme 39). 

The copolymerization, product was hyperbranched with the germole rmits dispersed throughout the product. A product yield of about 50% with a MWA of about 5200 was obtained. The hyperbranched material (Scheme 40) is soluble in organic solvents such as toluene. TGA analysis shows no weight loss to about 350°C and 60% residue to 800°C, which is consistent with ceramization upon pyrolysis. 

Aerts [63] modeled the intrinsic viscosity of dendritic and hyperbranched materials. 

If stars or dendrimers contain functional groups on the terminals of the arms, they react much faster than linear polymers to form thermoset coatings. Figure 9 shows schematic drawings of linear, branched, star, and hyperbranched (or dendritic) polymers. (Dendritic polymers are special hyperbranched materials with very ordered stractures.)... 

In order to compare general properties of hyperbranched polymers and dendrimers, Wooley et al. examined a model hyperbranched polyester and corresponding dendrimer. Pol)miers prepared from 3-hydroxy-5-( eri-butyldi-methylsiloxy)benzoic acid, as branching point, showed that thermal properties, such as Tg and those shown by thermogravimetic analysis (TGA), were independent of pol)mier architecture. However, the dendritic and hyperbranched materials demonstrated comparative solubilities that were much greater than that found for the linear polymer [99]. Their conclusions on the thermal properties may contradict some other findings. For examples, the of hyper-... 

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