Isophthalate ester-terminated dendrimers: Versatile nanoscopic building blocks with readily modifiable surface functionalities

The preparation and modification of highly functionalized polyether dendrimers containing a versatile diethyl isophthalate terminal group is presented. The convergent synthesis consists of the construction of diester-terminated dendrons containing benzylic bromide functions at the focal point and their subsequent attachment to 4,4'-biphenol cores. Dendrons up to the third generation can be prepared using recrystallization alone as the primary means of purification, allowing the synthesis to be performed on the scale of tens to hundreds of grams. The third and fourth generation bidendron dendrimers (with 32 and 64 terminal ester functionalities, respectively) have been subjected to a variety of surface modification reactions including hydrolysis, ester interchange, and amide-ester interchange, many of which proceed with complete conversion of the functional groups and in high isolated yield. The addition of alcohols such as benzyl alcohol or a first generation 3,5-di(benzyloxy)benzyl alcohol dendron to the dendrimer surface serves to increase the generation number of the dendrimers by one or two in what amounts to a 'double convergent growth' approach. The analysis of these structurally precise dendrimers by matrix-assisted laser desorption ionization time of flight is described.