Hyperbranched polybenzenes

Kim and Webster laid the foundation for the first hyperbranched polyarenes ( polyphenylenes ) in the form of Suzuki-analogous aryl-aryl coupling. Micellar structures developed on this basis [39] are described in Section 4.1.8 (ionic den-drimers). 

Initial work based on the Diels-Alder reaction provided access to linear polybenzenes via copolymerisation (Fig. 4.22) [40]. Diethynylbenzene acts as dieno-phile, and bis(cyclopentadienone) as diene. 

Since [4+2] cycloaddition is not very susceptible to steric hindrance, this synthetic concept has meanwhile been increasingly used for the assembly of hyperbranched compounds [41]. A diene combining two dienophile functions in one molecule was used as AB2 monomer for polymerisation (Fig. 4.23). The diene function can then react with a triple bond of a second AB2 monomer to form pentaphenylbenzene units [30]. 

Carbon/oxygen-based (and Fr chet) dendrimers 4.1.6.1 Polyether dendrimers 

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Hyperbranched polymers of polybenzene type can be rendered water-soluble like the above-mentioned monodisperse species by introduction of carboxyl groups [62]. Starting from 3,5-dibromophenylboronic acid 1 as AB2 monomeric building block (Fig. 4.34), the polycondensate 2 was assembled in an aryl-aryl coupling analogous to Suzuki coupling in the presence of Pd(0), and subsequently reacted with carbon dioxide to form the hyperbranched compounds 3 with terminal carboxylate groups ... 

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