Structural characterization, hyperbranched

Yamaguchi N, Wang JS, Hewitt JM, Lenhart WC, Monrey TH (2002) Acid chloride-functionalized hyperbranched polyester for facile and quantitative chain-end modification one-pot synthesis and structure characterization. J Polym Sci A Polym Chem 40 2855-2867... 

AB2 reacts selectively with only one antagonist function of a second polyfunctional molecule, the other ones being protected81 (Fig. 5.16). The perfect hyperbranched molecules obtained according to that step-by-step process are called dendrimers. The degree of branching characterizes the structure of a hyperbranched polymer and has been defined by Hawker et al.82 as... 

Often in hyperbranched polymers obtained via SCVP, it is not possible to determine the DB directly via NMR analysis. Therefore, other methods, for example, viscosity measurements and light-scattering methods have to be used to confirm the compact structure of a hyperbranched polymer. Such characterizations of hyperbranched (meth)acrylates will be discussed in the next section. 

Well-defined complicated macromolecular structures require complex synthetic procedures/techniques and characterization methods. Recently, several approaches leading to hyperbranched structures have been developed and will be the focus of this section. The preparation of hyperbranched poly(siloxysilane) has been reported [198] and is based on methylvinyl-bis(dimethyl siloxysilane), an A2B type monomer, and a progressive hydrosi-lylation reaction with platinum catalysts. An appropriate hydrosilylation reaction on the peripheral - SiH groups led to the introduction of polymeric chain (PIB, PEO) or functional groups (epoxy, - NH2) [199]. 

Ferrocene-based Branched Polymers (Dendrimers). One of the topics in macromolecular chemistry is constituted by dendrimers, or hyperbranched macromolecules of tridimensional globular structure, the surface of which is characterized by a large number of functional groups, Scheme 4. Such functionalities impart to the molecules solubility, viscosity and thermal properties different from those of the common linear polymers.38c,d 44... 

In this context numerous changes were made. The chapter Properties of Polymers was revised and a new section Correlations of Structure and Morphology with the Properties of Polymers was added. The chapter Characterization of Macromolecules was revised and enlarged. 15 examples have been deleted as they did no longer represent the state of the art and/or were of minor educational value. Several new experiments (plus background text) were added, as, for example controlled radical polymerization - enzymatic polymerization - microemulsions - polyelectrolytes as superabsorbants - hyperbranched polymers - new blockcopolymers - high impact polystyrene - electrical conducting polymers. 

In the beginning, the term dendrimer , which was established by Tomalia in 1985 [42,43], described all types of dendritic polymers. Later a distinction based on the relative degree of structural control present in the architecture was drawn. Nowadays, many other types of dendritic architectures are known, even if most of them, however, have not yet been widely investigated and fully characterized. The term dendritic polymer involves four substructures (Fig. 2), namely dendrimers themselves, dendrons, random hyperbranched polymers, and dendrigraft polymers [44, 45],... 

Whereas the well-characterized, perfect (or nearly so) structures of dendritic macromolecules, constructed in discrete stepwise procedures have been described in the preceding chapters, this Chapter reports on the related, less than perfect, hyperbranched polymers, which are synthesized by means of a direct, one-step polycondensation of A B monomers, where x > 2. Flory s prediction and subsequent demonstration 1,2 that A B monomers generate highly branched polymers heralded advances in the creation of idealized dendritic systems thus the desire for simpler, and in most cases more economical, (one-step) procedures to the hyperbranched relatives became more attractive. 

Additional studies have focused on the structure, modification and characterization of hyperbranched poly(carbosilanes) synthesized via hydrosilylation. The structure of the hyperbranched polymer derived from methyldiallylsilane was examined using small-angle... 

Dendritic macromolecules exhibit compact globular structures which lead to their low viscosity in the melt or in solution. Furthermore, dendritic macromolecules are characterized by a very large number of available functional groups, which lead to unprecedented freedom for changing/tuning/tailoring the properties of these multivalent scaffolds via complete or partial derivatization with other chemical moieties. All these features have contributed to multidisciplinary applications of these unique macromolecular structures in recent years 6, 7). The development of efficient synthetic routes in recent years has given rise to a virtually unlimited supply of commercially available dendritic polymers, at very affordable price. The transport properties of hyperbranched and dendritic polymers have recently attracted attention as potentially new barrier and membrane materials 8-9). 

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