Synthesis and characterization of carborane functionalized dendronized polymers as potential boron neutron capture therapy agents

Dendronized carborane containing polymers were successfully synthesized by the "graft-from" approach using a divergent dendron growth up to the fourth generation. Nitroxide mediated polymerization (NMP) proved effective in polymerizing the carborane-functionalized styrenic monomer to produce a well defined polymer with high boron content (∼26% B by weight) and narrow polydispersity index (PDI < 1.1). Dendronization of the carborane functionalized polymer was achieved via deprotonation of the acidic carborane proton in the para position followed by reaction of the polyanion with a benzylidene protected bisMPA anhydride. Complete removal of the benzylidene protecting group was achieved by a combination of Pd-catalyzed hydrogenolysis and acid- catalyzed deprotection. This chemistry proved effective in the preparation of monodisperse, high-generation hydroxyl- terminated dendrons appended to the carborane-functionalized polymer backbone. The fourth generation polymer, [G-4]- (OH)16, having a molecular weight of 114 kDa, was found to be water soluble at a concentration of 1 mg/mL and afforded a B content of approximately 12% by weight. All of the products were characterized by NMR and SEC. © 2008 American Chemical Society.