Hyperbranched architecture

Polyester chemistry is the same as studied by Carothers long ago, but polyester synthesis is still a very active field. New polymers have been very recently or will be soon commercially introduced PTT for fiber applications poly(ethylene naph-thalate) (PEN) for packaging and fiber applications and poly(lactic acid) (PLA), a biopolymer synthesized from renewable resources (corn syrup) introduced by Dow-Cargill for large-scale applications in textile industry and solid-state molding resins. Polyesters with unusual hyperbranched architecture also recently appeared and are claimed to find applications as crosstinkers, surfactants, or processing additives. 

Model III More Complexly Shaped Hyperbranch Architectures. 87... 

Figure 4. Series of persistent and robust super high-spin organic macromolecules with dendritic nature having a hyperbranched architecture, 5, and a topology of a three-coordinated Cayley tree, 6.

The hyperbranched architecture does not always afford an advantage in toughness or viscosity compared with low-molar-mass thermoplastic modifiers. 

Repetitive coupling of acetylenes with aryl halides is an effective way to directly build hyperbranched architecture in a stepwise manner. This type of polycoupling is often catalyzed by palladium complexes in the presence of amines and has been widely used for the preparation of well-defined oligomers, linear polymers, and perfectly branched dendrimers [19,20]. 

The second method separates the functional groups into two monomers, which facilitates synthetic work and offers greater choices to monomeric structure. In the first step, A2 and B3 monomers couple together to form an AB2-type dimer that continues to react to form the hyperbranched architecture (Scheme 6). This is the case, only if the molar ratio of A2 to B3 is 1 1 and the initiation is considerably faster than the propagation [29]. It becomes immediately clear that the resultant structure is highly dependant on the type of monomers and the polymerization conditions. For the latter, it has been found that the mode of monomer addition plays a crucial role. Whereas the addition of a B3 monomer into a solution of A2 yields insoluble polymer gel, the opposite addition mode furnishes hyperbranched polymers with excellent solubility [30]. 

The comparable architecture and chemical functionality of dendrimers and hyperbranched polymers lead to similar applications for these two families of dendritic polymers. The main benetit in using hyperbranched polymers to replace dendrimers lies in their simpler synthesis, provided that the perfect structure of dendrimers can be sacrificed for their broadly distributed hyperbranched analogs. The one-pot syntheses require less time and resources, resulting in less expensive processes that make hyperbranched polymers excellent candidates for commercial applications. Pertinent to the hyperbranched architecture are applications as electronic, magnetic, and catalytic materials, as well as numerous uses in the biomedical field some of these are considered herein. 

Stiriba. S.-E. Kautr. H. Frey. H. Hyperbranched molecular nanocapsules Comparison of the hyperbranched architecture with the perfectly linear analogue. J. Am. Chem. Soc. 2002, 124 (33). 9698-9699. 

Dendritic and Hyperbranched Architectures. The first example of a PLL dendrimer synthesis vras patented hy Denkewalter et The authors described a divergent stepwise synthetic route starting from N -bis(Boc)-L-lysine benzhydrylamide. The dendritic macromolecule with a PDI close to 1 was built through repetitive coupling with a Boc-protected lysine derivative activated with p-nitrophenyl ester, followed by deprotection. Furthermore, dendritic PLL macromolecules were functionalized on the surface with arginine end-groups for insulin complexation. ... 

The synthesis of dendrimers is one of the most impressive achievements in synthetic polymer science where the precise reaction control, necessary in organic chemistry, is extended to the synthesis of macromolecules. In its simplest form, a den-drimer is composed of simple AB (n S 2) monomeric building blocks (where A and B represent different functional groups) that are covalently interconnected into a hyperbranched architecture with a large number of active chain ends (B-groups). Since their first introduction in the mid-1980s, by Tomalia et al and Newkome et al., a myriad of structures have been reported, exploiting known robust chemistries. ... 

High ligand density. The hyperbranched architecture of the dendrimer allows high ligand density as the generation increases. 

Stiriba, S.-E., Kautz, H., and Frey, H. (2002) Hyperbranched molecular nanoc sules comparison of the hyperbranched architecture with the perfect linear analogue. Journal of American Chemical Society, 124,9698—9699. 

Hyperbranched polymers containing an encapsulated single core moiety have qualified as an interesting alternative to den-drimers for analogous studies, since they resemble in a majority of their characteristics and are usually easily accessible by a convenient synthesis. Tian et al. used a modified triphenyla-mine as core for a conjugated hyperbranched polymer, where a direct influence of the hyperbranched architecture on UV-absorption and fluorescence properties of the core was observed. Furthermore, postpolymerization modification of the nitrophenyl ester core, subsequent to the formation of the dendritic structure, has been reported. 

Zhao, T, Zheng, Y., Poly, J., Wang, W. Controlled multi-vinyl monomer homopolymerization through vinyl oligomer combination as a universal approach to hyperbranched architectures. Nat. Commun. 4, Article number 1873 (2013)... 

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