Synthesis and characterization of water-soluble dendritic macromolecules with a stiff, hydrocarbon interior

Phenylacetylene dendrimers terminated with tert-butyl esters on their periphery up to the fifth generation were synthesized by a modified convergent growth protocol. A solid-state thermolytic process involving no solvents, reagents, or catalysts accomplished transformation of the tert-butyl esters to carboxylic acids. The carboxylic acid terminated dendrimers possessed solubility characteristics orthogonal to those of the tert-butyl esters. Capillary electrophoresis and electrospray mass spectrometry were used to characterize the carboxylate terminated dendrimers. These techniques suggested that some form of cross-linking between or within higher generation dendrimer molecules was occurring during the thermolysis reaction. To overcome this problem, a second series of dendrimers terminated with (2-[2-(2-methoxyethoxy)ethoxy]ethyl) esters on their periphery were prepared, enabling aqueous solution hydrolysis to produce the carboxylic acids. The dendrimers that resulted by this approach were found to be more homogeneous products.