The Dendritic State and Dendritic Effects
Before 1984, three classes of macromolecular architecture (i.e. linear, cross-linked, and branched) were widely accepted for construction of relatively polydisperse products of different molecular weights. Since that year, the “dendritic state” is acknowl
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The Dendritic State and Dendritic Effects
Before 1984, three classes of macromolecular architecture (i.e., linear, cross-linked, and branched) were widely accepted for construction of relatively polydisperse products of different molecular weights [13, 19, 32, 49, 57]. Since that year, the “dendritic state” is acknowledged as a new, fourth class of polymer architecture. It can be divided to five subclasses: random hyperbranched polymers, dendrigrafts, dendrons, dendrimers, and tecto(dendrimers) or megamers [9, 12, 16, 18, 19, 30, 32– 34,49,51,56–58,60,62]. Megamers are architectures/polymers [4,23,24] which were initially described as starburst polymers [61, 62] that are made using dendrimers as fundamental building blocks. They can be classified into two wide categories: statistical and structure-controlled megamers. In accord with Tomalia [49, 57] the precision architecture of dendrons/dendrimers allows these entities to be viewed as nanoscale monomer-type building blocks, which are suitable for the construction of regio-cross-linked dendrimers referred to as “megamers.” The synthesis of dendrimers (in contrast to synthesis of “prior” macromolecules) proceeds smoothly to monodisperse, structure-controlled macromolecular systems similar to those observed in nature [1, 3, 8, 9, 12, 17, 25, 32, 34, 43, 44, 46, 51, 56, 66]. Starting from commercially available chemicals, dendrimeric polymers with polydispersities of Mw =Mn 1.0005–1.05 are routinely obtained in multigram to kilogram scale [32,34,51,56]. This was enabled also by simplifications of their synthesis by Lego-, ligation, and click chemistries [44,49] (see also Chaps. 6.3, 6.4, and 6.5). Because of multistep dendrimer synthesis, the resulting dendrimer material is always a mixture of both ideal and nonideal structures [6, 9, 25, 43]. Dendrimers and hyperbranched polymers are partly overlapping groups [3, 17, 25, 43, 46, 60, 66], which differ in regularity of structure, synthetic availability, and chemical variability. In comparison with hyperbranched polymers, dendrimers are more regular and better defined, but more difficult to prepare (more expensive). It is very probable that the role of hyperbranched polymers will grow whereas the role of dendrimers will be shifted more to the field of fine chemicals. This book deals mainly with the topic of dendrimers with highlights of more important discoveries in the field of hyperbranched polymers. ˇ J. Sebest´ ık et al., Biomedical Applications of Peptide-, Glyco- and Glycopeptide Dendrimers, and Analogous Dendrimeric Structures, DOI 10.1007/978-3-7091-1206-9 5, © Springer-Verlag Wien 2012
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5 The Dendritic State and Dendritic Effects
Due to the presence of a large number of terminal groups and the limitations or a complete lack of interpenetration, the physicochemical properties of dendrimers differ from those of classical polymers [6, 12]. The fundamental properties of dendrimers are [7, 8, 25, 49–51, 56, 58, 60, 63, 67]: (1) The nanometer dimensions which are similar to the size of crucial biomacromo
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