Polymer architecture classes

More recently, nontraditional polymerization strategies have evolved to produce a fourth new major polymer architectural class, now referred to as dendritic polymers. This new architectural polymer class consists of four major subsets, namely (a) random hyperbranched, (b) dendrigrafts, (c) dendrons, and (d) dendrimers. Dendrimers, the most extensively studied subset, were discovered by the Tomalia group while at The Dow Chemical Company laboratories (1979). They represent the first example of synthetic, macro-molecular dendritic architecture [33,34]. First use of the term dendrimer appeared in preprints for the 1st SPSJ International Polymer Conference held in Kyoto, Japan (1984). The following year, a full article Polymer Journal, Vol. 17, No. 1, pp. 117-132 (1985)) (see article abstract. Fig. 42.7) described the first preparation of a complete family of... 

Figure 1.3 Historical discovered and production dates of commercial thermoplastic and thermoset polymers organized according to their architectural class...

Figure 1.7 Examples of architectural polymer classses (I—IV) polymer type, repeat units and covalent connectivity associated with architectural classes...

DENDRITIC POLYMERS-A FOURTH MAJOR NEW ARCHITECTURAL CLASS... 

Since that time, synthetic chemists have explored numerous routes to these statistically hyperbranched macromolecular structures. They are recognized to constitute the least controlled subset of structures in the major class of dendritic polymer architecture. In theory, all polymer-forming reactions can be utilized for the synthesis of hyperbranched polymers however, in practice some reactions are more suitable than others. 

Dendritic polymers, the fourth major architectural class of macromolecules, can be divided into three subclasses. These subclasses may be visualized according to the degree of structural perfection attained, namely (1) hyperbranched polymers (statistical structures, Chapter 7), (2) dendrigraft polymers (semi-controlled structures, reviewed in this chapter) and (3) dendrimers (controlled structures, Chapter 1). 

Figure 11.7 illustrates the three different subtypes of dendritically branched molecules that have been identified within the major architectural class of dendritic polymers. Random hyperbranched polymers, not only exhibit polydispersity in molecular mass between individual molecules, it should also be noted... 

Amphiphilic polymers studied thus far for this purpose can be broadly classified into amphiphilic block copol5mers and amphiphilic homopolymers. We will discuss both of these types of linear polymer architectures. Another interesting class of polymeric amphiphiles is based on branched architectures, known as dendrimers. The most interesting aspect of dendrimers is that their molecular weight and polydisper-sity can be precisely controlled hence, these systems have the potential to be moved... 

Nitroxide-Mediated Controlled Radical Polymerization (NMCRP) was first discovered by Solomon et al., who patented their discovery in 1985 [205]. This opened up new pathways in the field of free-radical polymerization. Polymer architectures, which were the domain of the anionic polymer chemist, became accessible to the free-radical polymer chemist. However, it was not until the work of Georges et al. [206] was published in 1993, that the world of polymer chemistry became aware of the possibihties of this new class of free-radical polymerization. This was the beginning of what is today one of the leading topics in free-radical polymer chemistry Controlled or Living Free Radical Polymerization. This initiated the search for new Controlled or Living Free Radical Polymerization techniques, and soon afterwards other methods (which will be discussed later) were developed. 

Dendrimeric molecules, also known as cascade molecules or Starburst molecules, represent an architectural class of macromolecules different from both ordinary polymers of the linear or cross-linked classes and biopolymers of the carbohydrate or peptide classes. 

Fig. 3 Schematic representations of some possible supramolecular liquid crystalline polymer architectures, a-e Different classes of main-chain structures, f-i Different side chain polymers, j-m Different types of networks...

Synthetic polymers can be divided into four key architectural classes linear, crosslinked, branched and dendritic structures. The first three types have been studied extensively in the past. The fourth comprises the more recently developed, nature-inspired dendrimers, and derivatives. 

The surfactant properties of macromolecules (and hence their ability to self-assemble into functionally interesting motifs) can be controlled with high sensitivity by manipulating molecular architecture without changing the chemical identity of the amphiphilic moieties. In addition to differences in surfactant properties between macromolecules in different architectural classes, subtle variations in an architectural class also lead to significant effects. This is due to the importance of conformational entropy for self-assembly processes of polymers. This notion of choosing the nature of the connections between the amphiphilic moieties to control surfactant properties may prove useful in applications where the choice of chemical structure is restricted (e.g., for concerns related to biocompatibility or toxicity). 

Dendritic polymers are expected to play a key role as enabling building blocks for nanotechnology during the 21st century, just as the first three traditional architectural classes of synthetic polymers have so successfully fulfilled critical material and functional needs in the plastics age during the past half century. The controlled shape, size,... 

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