Polyhedral Oligomeric Silsesquioxane 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 core. Dendrimers based on POSS were first reported in 1993 and have resulted in many publications to date [4].

Siloxanes are molecules with the general formula [RSiO_x/2] where R is an organic group or silicon species. Siloxanes may be discrete molecules, two-dimensional ladders or networks, or three-dimensional cages or polymers. The siloxane linkage, Si–O–Si is formed when different units join to form larger molecules. Siloxy groups [R₃SiO_1/2] are good terminal groups because they halt formation of larger siloxane networks, siloxane [R₂SiO_2/2] groups are ideal candidates for forming long chain-like molecules, while silsesquioxanes [RSiO_3/2] and silicates [SiO_4/2] are most commonly found in three-dimensional structures, both random polymers and oligomers, due to the number of siloxane linkages that can be created. In all cases, a large number of structures with a large number of functionalities have been reported [5]