Dendrimers macromolecular architecture

Polyamidoamine (PAMAM) dendrimers have drawn considerable interest in recent years due to their potential applications in medicine, nanotechnology, and catalysis (6,7). The ability to control dendrimer interior/exterior functionalities and the macromolecular architecture of PAMAM dendrimers... 

The history of dendrimer chemistry can be traced to the foundations laid down by Flory [34] over fifty years ago, particularly his studies concerning macro-molecular networks and branched polymers. More than two decades after Flory s initial groundwork (1978) Vogtle et al. [28] reported the synthesis and characterization of the first example of a cascade molecule. Michael-type addition of a primary amine to acrylonitrile (the linear monomer) afforded a tertiary amine with two arms. Subsequent reduction of the nitriles afforded a new diamine, which, upon repetition of this simple synthetic sequence, provided the desired tetraamine (1, Fig. 2) thus the advent of the iterative synthetic process and the construction of branched macromolecular architectures was at hand. Further growth of Vogtle s original dendrimer was impeded due to difficulties associated with nitrile reduction, which was later circumvented [35, 36]. This procedure eventually led to DSM s commercially available polypropylene imine) dendrimers. 

Will these emerging megameric structures of poly(dendrimers) represent a new class of macromolecular architecture with unique properties and characteristics ... 

Nevertheless, the existence of the famed maximum in the dendrimer [>7] vs G relationship, and whether this behavior could be a characteristic fingerprint property of this type of macromolecular architecture, was questioned recently [19, 23], In fact, so was the linearity of the dependence of dendrimer molecular radii on M1/3 [19], so that whether this may be the beginning of yet another controversy, remains to be seen. Perhaps the future may bring an interesting debate on these subjects, but until new data become available, one should refrain from drawing premature conclusions because the exciting architectural beauty of idealized dendrimer structures has already proven itself to easily tempt the most astonishing hypotheses that may not be readily substantiated by reality. 

Lee, S. C. 2000. Dendrimers in nanobiological devices, in Tomalia, D. and Frechet, J. M. J. (eds). Dendritic Polymers-A New Macromolecular Architecture Based on the Dendritic State, John Wiley Sons, in press. 

The book consists of four articles reviewing the literature based on the authors own experiences over the last decade in this field. It does not claim to be exhaustive nor to provide complete coverage of the very extensive literature in this field. Instead, it focuses on the currently intense areas of research namely living polymerization, block copolymer synthesis, synthesis of dendrimers and finally macroporous thermosets. Hopefully, this volume will not only serve as a book on the design of macromolecular architectures but also as a source of inspiration to produce polymers combining several functional properties. 

As defined, dendritic networks are considered to result from the one-, two-, and three-dimensional orientation of dendrimers thus ordering can be geometrically likened to rods surfaces or sheets and cubes, tetrahedrons, or spheres, respectively. Due to the broad scope and breadth of potential macromolecular architectures that can be obtained by application of different modes of connectivity, we will herein concentrate on networks constructed from the simplest dendritic structures, namely those that are pseudospheri-cal or globular. The principles that are presented here pertaining to network formation should be easily adaptable to non-spheroidal dendritic structures as well as macromolecular assemblies possessing only limited dendritic character. 

D. A. Tomalia, Birth of a New Macromolecular Architecture Dendrimers as Quantized Building Blocks for Nanoscale Synthetic Organic Chemistry. Aldrichimica Acta 2004, 37(2), 39-57. 

Tomalia, D. A., et al. (1991), Comb-burst dendrimer topology. New macromolecular architecture derived from dendritic grafting, Macromolecules, 24,1435-1438. 

Figure 1 Macromolecular architectures linear macromolecular chains (homopolymer, block-copolymer and statistical copolymer [14]), brushed-polymer (= linear chains attached to a polymer-chain brush-polymer, brush-copolymers [14]), star polymer [4], mikto-star-polymer [16], arborescent graft polymer (=repeated grafting of linear chains on a macromolecule [17,18]), dendrimer (= maximally branched, regular polymer [15])...

Recently the development of dendritic and hyperbranched polymers (HBPs) has attracted much attention (Tomalia, 1985, Newkome et al, 1985, Webster, 1991, Chu and Hawker, 1993, Wooley et al, 1994, Feast and Stanton, 1995, Malmstrom et al, 1995, Kim, 1998). The key features of the macromolecular architecture of dendrimers and HBPs are given in Section 1.2, and their synthesis by stepwise polymerization is discussed in Section 1.2.1. Dendrimers and HBPs are globular macromolecules that have a highly branched structure with multiple reactive chain ends (shell), which converge to a central focal point (core) see Figure 5.1, where I is the core, 11 is the structure and 111 is the shell. 

PROPERTIES OF SPECIAL INTEREST Unique dendrimer properties not found in traditional macromolecular architecture include (1) a distinct parabolic intrinsic viscosity curve with a maximum as a function of molecular weight (2) very... 

Three-dimensional branched architectures, generally termed dendrimers, represent a class of synthetic macromolecules that have impacted dramatically on the field of organic and polymer chemistry and created a new branch in synthetic and material chemistry. For the last two decades, dendrimer research has been at the forefront of polymer research and was first postulated in the 1940s by Flory, a pioneer in polymer research and Nobel Laureate in 1974, who proved the existence of branched chains and their potential role in three-dimensional (3D) macromolecular architectures [446-448], In 1978, Vogtle et al. developed an iterative cascade method for the synthesis of low molecular weight branched amines [449]. The real expansion of the field started after Tomalia et al. [450] and Newkome et al. [451] discovered the starburst effect, which shed light on a new chemical arena. Since then, dendrimer chemistry has been diversified... 

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