Dendrigraft polymers: macromolecular engineering on a mesoscopic scale

Dendrigraft polymers are a class of highly branched macromolecules belonging to the dendritic polymer family. Multiple branching levels characterize the architecture of these molecules, in analogy to dendrimers and hyperbranched polymers. The size of dendrigraft polymers is typically 1-2 orders of magnitude larger than for their dendritic counterparts, however, ranging from around 10 nm to a few hundred nanometers. Dendrigraft polymers exhibit many of the physical properties characteristic of dendritic molecules on a mesoscopic scale. Another main distinguishing feature of these polymers is their synthesis, based on grafting reactions with polymeric side chains serving as building blocks. Dendrigraft polymers may be viewed as semi-controlled branched polymer architectures intermediate in terms of structure control between dendrimers and hyperbranched polymers. They most often incorporate randomly distributed branching points, but are still characterized by narrow molecular weight distributions. The synthesis and physical properties of dendrigraft polymers are reviewed herein. Three distinct synthetic methodologies are considered for the preparation of these materials: (1) divergent 'grafting onto' methods based on successive coupling reactions of polymer chains with a functionalized substrate polymer, (2) divergent 'grafting from' methods using cycles of polymerization initiated from functional sites located on a substrate polymer, and (3) convergent 'grafting through' methods involving coupling of preformed polymer chains in a one-pot reaction. Interesting properties reported for dendrigraft polymers are also discussed, as well as some suggestions for potential applications. (C) 2004 Elsevier Ltd. All rights reserved.