Dendritic macromolecules architectures

In 1996, Hawker and Frechet83 discussed a comparison between linear hyperbranched and dendritic macromolecules (Fig. 5.17) obtained with the same monomeric structure, 3,5-dihydroxybenzoic. The thermal properties (glass transition and thermal decomposition) were not affected by the architecture. 

C. J. Hawker and J. M. J. Frechet, Preparation of polymers with controlled molecular architecture. A new convergent approach to dendritic macromolecules, J. Am. Chem. Soc., 112 (1990) 7638-7647. 

Flory was the first to hypothesize concepts [28,52], which are now recognized to apply to statistical, or random hyperbranched polymers. However, the first purposeful experimental confirmation of dendritic topologies did not produce random hyperbranched polymers but rather the more precise, structure controlled, dendrimer architecture. This work was initiated nearly a decade before the first examples of random hyperbranched4 polymers were confirmed independently in publications by Odian/Tomalia [53] and Webster/Kim [54, 55] in 1988. At that time, Webster/Kim coined the popular term hyperbranched polymers that has been widely used to describe this type of dendritic macromolecules. 

The same reasons for the interest in incorporating ferrocene units into polymers also provided motivation for the synthesis of dendritic macromolecules of well-defined size and structure containing ferrocenyl units. An important additional rationale for the construction of ferrocenyl dendrimers is provided by the fact that such macromolecules raise the possibility of combining the unique and valuable redox properties associated with the ferrocene nucleus with the highly structured macromolecular chemistry. This may provide access to materials of nanoscopic size possessing unusual symmetrical architectures, as well as specific physical and chemical properties which would be expected to differ from those of the ferrocene-based materials prepared to date. 

The synthesis and bulk and solution properties of block copolymers having nonlinear architectures are reviewed. These materials include star-block copolymers, graft copolymers, mik-toarm star copolymers, and complex architectures such as umbrella polymers and certain dendritic macromolecules. Emphasis is placed on the synthesis of well-defined, well-characterized materials. Such polymers serve as model materials for understanding the effects of architecture on block copolymer self-assembly, in bulk and in solution. 

C.J. Hawker and J.M.J. Fechet, Preparation of polymers with controlled molecular architecture. A new covergent approach to dendritic macromolecules, J. Am. Chem. Soc., 1990, 112, 7638 F. Zeng and S.C. Zimmerman, Dendrimers in supramolecular chemistry from molecular recognition to self-assembly, Chem. Rev., 1997, 97, 1681 D.J.P. Yeardley, G. Ungar, V. Percec, M.N. Holerca and G. Johnsson, Spherical supramolecular minidendrimers self-organized in an inverse micellar -like thermotropic body-centered cubic liquid crystalline phase, J. Am. Chem. Soc., 2000, 122, 1684. 

Dihydroxybenzyl aicohoi has been employed as starting intermediate for the synthesis of new poiymeric systems, dendritic macromolecules (fan-like structures) or molecules with controiied moiecular architecture (ref.128). It is readily obtained by the lithium hydride reduction of 3,5-dihydroxybenzoic acid. 

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. ... 

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