Synthesis of dendritic polymers – a fourth major new architectural class

In traditional small molecule chemistry it is widely recognized that their structures may be categorized architecturally as: (I) linear, (II) bridged, and (III) branched types as shown in Figure 3.1. Seminal work by Vögtle and Buhleier [1] provided first examples of new non-traditional cascade type molecules. These structures are now recognized as small molecule examples of a fourth new architectural type, namely dendritic molecules. Since the introduction of Staudinger’s macromolecular hypothesis in the 1920s, three major polymer architectures have defined all traditional polymer types. Paralleling small molecule chemistry, all traditional macromolecular architectures were categorized into three major types, namely; (I) linear, (II) cross-linked (bridged) and (III) branched structures. Since the early 1980s these traditional polymer architectures have been joined by a fourth new major class of macromolecular architecture, namely dendritic macromolecules [2, 3]. This fourth class of dendritic polymers was distinguished from traditional polymer types, based on new intrinsic properties [2, 4–6]. These new properties are unlike any of those found in the three traditional architectural types and are often referred to as “dendritic effects” (see Chapter 7).

A multitude of synthetic strategies has been reported for preparation of dendritic materials since their discovery in the late 1970s-early 1980s and this has led to a broad range of methodologies and structures. Presently, this dendritic architectural class consists of four subclasses, namely: (IVa) random hyperbranched polymers, (IVb) dendrigraft polymers, (IVc) dendrons, and (IVd) dendrimers (Figure 3.2). The order of these subsets, Figure 3.2 from (a) to (d), reflects the polydispersity associated with the methodologies to produce each of these subsets and may be generally referred to as: (IVa) statistical, (IVb) semi-controlled and (IVc,d) controlled dendritic structures [7, 8].