The microstructure of monomers affects the material properties of polymers made from them. While linear (e.g. ethylene) and cyclic (thiophene) monomers are ubiquitous in polymer chemistry, 3-dimensional monomers (molecular cages) are minimally represented. This is because most monomers are constructed from hydrocarbon frameworks, and making well-defined cages from hydrocarbons is challenged by the high strain inherent to short and rigid C-C bonds. For the same reason, macromolecules made from simple organic cages also exhibit poor solubility. Thus, cage-dense materials remain difficult to access, primarily due to a lack of readily available and solubilizing monomers. We recognized that the inorganic p-block elements readily form unstrained cages that are thermodynamically stable and kinetically accessible. The longer, more flexible, bonds found in such compounds can also enhance solubility (e.g. polysiloxanes). We now reveal a family of inexpensive and easily prepared phosphorus-nitrogen molecular cages that have nucleophilic termini suitable for polycondensation reactions with electrophilic linkers. These polycondensations yield high-molecular weight, solution processeable, polymers that exhibit good ambient stability and excellent tunability on the linker side, permitting incorporation of several inorganic elements into the polymer backbone. The cages-dense PNX (X = linker element) polymers can also be crosslinked to generate porous networks and shape persistent objects. The synthesis, polymerization kinetics, and material properties of these new PNX cage materials will be described.

PN cages as modular entry points into cage-dense inorganic materials

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