Chemistry Reference
In-Depth Information
SCHEME 2.6
Building blocks for the discrete supramolecular dendrimers.
polyamides are commonly available as engineering plastic materials with high
modulus due to semicrystallinity or high glass transition temperatures. However, the
semicrystallinity and the strong tendency to form hydrogen bonding cause low
solubility, high melting point, and limiting the processing. A highly branched
structure such as dendrimers, which is usually amorphous materials with excellent
solubility and low viscosity, might improve the processing of polyamides. Thus, the
introduction of dendritic structure into polyamides will result in new applications as
an engineering plastic.
Although various synthetic methods have been developed to prepare dendrimers
containing amide functions, they have problems such as poor yield and tedious
multisynthetic steps [21]. Kakimoto and coworkers [21d] developed an orthogonal
synthesis to poly(aryl amide) dendrimers (Scheme 2.7). Condensation of the first
AB
2
-building block, 3,5-diaminobromobenzene, with a carboxylic acid G1-COOH
yielded a dendritic bromide G2-Br. Dendron G2-Br could then be activated by a
palladium-catalyzed insertion of carbon monoxide, enabling the reaction with the
second AB
2
-building block, 3,5-diaminobenzoic acid, to yield a dendritic carboxylic
