Chain-end-functionalized polyphosphazenes via a one-pot phosphine-mediated living polymerization.

A simple polymerization of trichlorophosphoranimine (Cl3 P = N-SiMe3 ) mediated by functionalized triphenylphosphines is presented. In situ initiator formation and the subsequent polymerization progress are investigated by (31) P NMR spectroscopy, demonstrating a living cationic polymerization mechanism. The polymer chain lengths and molecular weights of the resulting substituted poly(organo)phosphazenes are further studied by (1) H NMR spectroscopy and size exclusion chromatography. This strategy facilitates the preparation of polyphosphazenes with controlled molecular weights and specific functional groups at the α-chain end. Such well-defined, mono-end-functionalized polymers have great potential use in bioconjugation, surface modification, and as building blocks for complex macromolecular constructs.

Thermoresponsive Polyphosphazene-Based Molecular Brushes by Living Cationic Polymerization.

A series of polyphosphazenes with molecular brush type structures have been prepared with controlled molecular weights and narrow polydispersities. The polymers show lower critical solution temperatures (LCST) between 18 and 90 °C, which can be easily tailored by choice of side-substituent to suit the required application. A temperature triggered self-assembly is observed to give stable colloidal aggregates with dimensions in the region of 100-300 nm.

Water-Soluble, Biocompatible Polyphosphazenes with Controllable and pH-Promoted Degradation Behavior.

The synthesis of a series of novel, water-soluble poly(organophosphazenes) prepared via living cationic polymerization is presented. The degradation profiles of the polyphosphazenes prepared are analyzed by GPC, 31P NMR spectroscopy, and UV-Vis spectroscopy in aqueous media and show tunable degradation rates ranging from days to months, adjusted by subtle changes to the chemical structure of the polyphosphazene. Furthermore, it is observed that these polymers demonstrate a pH-promoted hydrolytic degradation behavior, with a remarkably faster rate of degradation at lower pH values. These degradable, water soluble polymers with controlled molecular weights and structures could be of significant interest for use in aqueous biomedical applications, such as polymer therapeutics, in which biological clearance is a requirement and in this context cell viability tests are described which show the non-toxic nature of the polymers as well as their degradation intermediates and products.

Branched Polyphosphazenes with Controlled Dimensions.

Using living cationic polymerization, a series of polyphosphazenes is prepared with precisely controlled molecular weights and narrow polydispersities. As well as varying chain length through the use of a living polymerization, amine-capped polyalkylene oxide (Jeffamine) side chains with varied lengths are grafted to the polymer backbone to give a series of polymers with varied dimensions. Dynamic light scattering and size exclusion chromatography are used to confirm the preparation of polymers with a variety of controlled dimensions and thus hydrodynamic volumes. Furthermore, it is demonstrated how the number of arms per repeat unit, and thus the density of branching, can also be further increased from two to four through using a one-pot thiolactone conversion of the Jeffamines, followed by thiol-yne addition to the polyphosphazene backbone. These densely branched, molecular brush-type polymers on a biodegradable polyphosphazene backbone all show excellent aqueous solubility and have potential in drug-delivery applications.