The synthesis, characterization, and properties of stiff, hydrophilic, dendritic, phenylacetylene macromolecules

A series of phenylacetylene dendrimers bearing t-butyl ester groups on their periphery were prepared by a modified convergent growth scheme. The structures of these organic soluble compounds were confirmed by a variety characterization techniques including NMR, mass spectrometry, elemental analysis, GPC, and HPLC. Careful analysis of an apparently pure dendrimer revealed the presence structures incorporating small quantities of isopropyl esters derived from a trace impurity in the monomer. Conversion of the t-butyl esters to carboxylic acids was accomplished by an efficient solid-state thermolytic process which required no solvents, reagents or catalysts. The resulting dendrimers were soluble in aqueous base, but much more difficult to characterize owing to their solubility in a limited number of solvents. Electrospray ionization mass spectrometry and capillary electrophoresis were useful methods to probe structure and sample homogeneity, respectively. The higher generation carboxylic acid terminated dendrimers appeared to be lightly crosslinked as a result of the thermolysis reaction. Carboxylate terminated tridendrons were shown to solubilize perylene and toluene in aqueous solution. A second series of dendrimers were prepared with 2- (2-(2-methoxy-ethoxy)-ethoxy) ethyl ester groups on their periphery. Solution phase hydrolysis under basic conditions was employed to convert the esters to carboxylates. A high generation dendrimer prepared by this process was observed to be homogeneous by capillary electrophoresis. The 2- (2-(2-methoxy-ethoxy)-ethoxy) ethyl ester terminated tridendrons exhibited hexagonal columnar discotic mesophases. Finally, a series of asymmetric tridendrons containing a large lipophilic domains and hydrophilic domains of varying size were prepared. Aggregation of these macromolecular amphililes in lipophilic solvents was studied.