MACROMOLECULAR AND MOLECULAR CHEMISTRY OF PHOSPHORUS-NITROGEN CAGES AND RINGS

Abstract

A new class of main group polymers containing three-dimensional phosphorus-nitrogen (PN) cage motifs in the backbone are described in this work. The PN cages prepared are rigid, robust but amenable to metathesis chemistry with high chemoselectivity, providing access to high molecular weight macromolecular material with cages installed within the polymer backbone. The stability, reactivity, and molecular structure of the PN cages are assessed. The polymers that result from the reaction of PN cages monomers with p-block element dihalides are assessed, giving new insights into the orthogonal reactivity of PN cage-containing polymers, the influence of the rigid cage backbone on the polymer microstructure, and the thermal properties that result. Mechanistic studies reveal a previously unknown chain-transfer step-growth mechanism mediated by the formation of phosphino-phosphonium intermediates. Design principles for constructing polymers with PN cage backbones emerge from attempts to expand the library of p-block comonomers available to copolymerize with the cages. An understanding of the influence of the three-dimensional cage geometry on the PN monomers is further gleaned from the preparation of a two-dimensional analogue to a PN cage monomer and attempts to polymerize it with suitable comonomers. Viewed as a whole, these results yield new insights into the effect of polymer backbone dimensionality on polymer properties and provide a “tool-kit” for facile access of polymers with three-dimensional cages in the backbone.