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During the last two decades, dendritic polymers, particularly dendrimers and hyper-branched polymers, have become one of the fastest growing areas of interest in polymer science [1]. This can be easily seen from the impressive growth in the number of publications on these unique polymers, which soared from less than a dozen in the 1970s, to over 10,000 (in scientific journals and patent literature)...
Three different original protocols for the synthesis of siloxane dendrimers have been described. However, after appearing in the literature at much the same time they did not result in any follow-up, unlike many other strategies proposed simultaneously or even later. To appreciate the suddenness of the introduction of siloxane dendrimers and the reasons for their subsequent neglect we need to make...
The concept of highly symmetrical, perfectly branched macromolecules prepared in a generational fashion was introduced in 1978 [1]. The synthesis of polylysine dendrimers [2] and the seminal research by Tomalia and Newkome in the mid-1980s established that such molecules could indeed be prepared [3, 4]. Tomalia et al. used trifunctional nitrogen branch points and Newkome chose tetrafunctional carbon...
Polysilanes, –(Si)n–, are polymers that contain catenated silicon atoms, and their chemistry has attracted considerable interest during the last 30 years because of their electronic, optical, structural, and chemical properties [1]. In particular, the σ-conjugation of the –Si–Si– backbone has attracted much attention compared with analogous carbon polymer systems. Although, in contrast to the numerous...
Linear polysilazanes and polycarbosilazanes are well-known members of the organosilicon polymer family and can be prepared by a variety of methods [1, 2]. These polymers are characterized by having either a –Si–N– backbone (polysilazanes) or a –R–Si–N– backbone (polycarbosilazanes). On the other hand, dendritic analogs are relatively rare. Polysilazane dendrimers are essentially nonexistent, and the...
About three decades ago a remarkable cascade-type molecule was reported by Vögtle and his co-workers [1, 2]. This development set the stage for new types of polymers with a high degree of isomolecularity that are now widely known as dendrimers (see Chapter 1). In the years that followed, a number of different compositions of dendrimers, including amidoamine-, ether-, amine-, and ester-type dendrimers,...
Dendrimers have been prepared with a wide variety of core molecules since the first patents and publications in the early 1980s (see Chapter 1) [1–3]. The most common core molecules (e.g. ammonia, ethylenediamine, pentaerythritol) permit 2–4 branches although some molecules may give greater branch multiplicity. Polyhedral oligo-meric silsesquioxanes (POSS) allow eight branches to radiate from a silicon-oxygen...
Dendrimers constitute a unique class of macromolecular architectures that differs from all other synthetic macromolecules in its perfectly branched topology, which is constructed from a multifunctional central core and expands to the periphery that becomes denser with increasing generation number (see Chapter 1) [1–5]. Since the pioneering works published in the late 1970s and the mid-1980s [6–8],...
The attachment of catalytic species to support materials is a widely applied method to combine the advantages of homogeneous and heterogeneous (supported) catalysis. The commonly used organic supports are insoluble polymeric materials, which have been developed with great success for solid phase organic synthesis and have a long history and importance. Obvious difficulties with these materials are...
It is well-known that one of the main features of low-molar-mass liquid crystals and liquid-crystalline (LC) polymers is the presence of anisometric molecular fragments (mesogenic groups) responsible for LC phase (mesophase) formation. The majority of mesogenic groups consist of rigid rod-, board- (or lath-) and disk-shaped molecular moieties, which play a role of specific “building blocks”, a spontaneous...
Silicon can play a variety of different roles when incorporated in or combined with otherwise “purely” organic dendritic branch cells which in this chapter are meant to include those that contain carbon and some combination of hydrogen, nitrogen, oxygen and sulfur. As a result, a diversity of compositional and architectural hybrid dendrimers can be formed, containing one or more of the following types...
Nucleophilic substitution reactions involving organomagnesium (Grignard) [1] and organolithium reagents have been used extensively for many years to form Si—C bonds (see Reaction Scheme 12.1). However, their use for the construction of hyperbranched polymers whose backbone contains, as a major structural component, silicon—carbon bonds, i.e., polycarbosilanes [2] is relatively more recent. (12.1)...
As pointed out in Chapter 1, silicon chemistry offers a variety of quantitative, high yielding reactions, i.e. hydrosilylation, Grignard reactions and controlled condensation of silanols that are suitable for the synthesis of organic-inorganic hybrid materials. Thus, silicon-based chemistry played a prominent role in the evolution of dendrimer chemistry [1–4], and it did not take long until the first...
Recent developments in the control of macromolecular architecture have led to important progress in dendritic structures, such as dendrimers and hyper-branched polymers, which exhibit fundamentally different properties from their linear counterparts, including impeded crystallization, minimized chain entanglements, unusual viscosity profiles and solubility behavior (see also Chapter 1). Furthermore,...
Theoretical descriptions of ABn (n ≥ 2) hyperbranched polymerization systems have been known for some time [1], but in them, cyclization is a factor that is generally and largely ignored. However, it is now understood that cyclization is prevalent in polymerizations of this type, and that it can often affect to a significant extent both polydispersity and molecular weights of the polymer products...
Bimolecular non-linear polymerization, BMNLP (see Reaction Scheme 16.1), represents ‘the other method’ for preparation of hyperbranched polymers by the step-growth reaction mechanism. In contrast to the monomolecular polymerizations of ABx monomers, discussed for the two most prominent groups of silicon-containing hyperbranched polymers in Chapters 12 and 13, this polymerization type involves, as...
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