Polyphosphazene Based Star-Branched and Dendritic Molecular Brushes

Abstract

A new synthetic procedure is described for the preparation of poly(organo)phosphazenes with star-branched and star dendritic molecular brush type structures, thus describing the first time it has been possible to prepare controlled, highly branched architectures for this type of polymer. Furthermore, as a result of the extremely high-arm density generated by the phosphazene repeat unit, the second-generation structures represent quite unique architectures for any type of polymer. Using two relativity straight forward iterative syntheses it is possible to prepare globular highly branched polymers with up to 30 000 functional end groups, while keeping relatively narrow polydispersities (1.2-1.6). Phosphine mediated polymerization of chlorophosphoranimine is first used to prepare three-arm star polymers. Subsequent substitution with diphenylphosphine moieties gives poly(organo)phosphazenes to function as multifunctional macroinitiators for the growth of a second generation of polyphosphazene arms. Macrosubstitution with Jeffamine oligomers gives a series of large, water soluble branched macromolecules with high-arm density and hydrodynamic diameters between 10 and 70 nm. A route to previously unattainable branched polyphosphazenes with controlled dimensions is presented. Furthermore, the star branched polyphosphazenes undergo macromolecular substitution with diphenylphosphine groups which can act as macroinitiators for the grafting of a second generation of polyphosphazenes. This subsequently gives dendritic molecular brush type structures with novel, highly branched, water-soluble, globular architectures.