Surface Functionalization with Phosphazene Substrates. Part II. Theoretical and Experimental Investigations of the Interactions of Hexachlorocyclophosphazene with Hydroxylated Silicon-based Surfaces

The interaction of hexachlorocyclophosphazene (HCCP) with the hydroxylated silicon-based surfaces is studied by a combination of XPS experimental analysis and theoretical ab initio simulations, including the estimate of the energy barriers via CI-NEB method to determine the minimum energy reaction paths. Several possible, stable chemisorbed configurations are found to exist, whose structural, energetic, and electronic properties have been analyzed in detail. The theoretical results are in good qualitative agreement with available experimental data. In particular, we get indications that water plays a crucial role in the surface functionalization with HCCP, although the presence of a suitable solvent (e.g. tetrahydrofuran, THF) seems to be essential. This paper is dedicated to Prof. Harry R. Allcock and the pioneering discoveries of his research group particularly in polyphospazenes and generally in materials science.     

Synthesis of functionalized multiarm poly(ethylene oxide) stars

Six arm poly(ethylene oxide) (PEO) stars carrying either 6 pyridyl or 12 hydroxyl groups at their periphery were synthesized using an arm-first approach. To this end, two novel α,ω-heterodifunctional PEO's, namely α-ketal,ω-hydroxy and α-pyridyl,ω-hydroxy PEO's were synthesized and, after the deprotonation of their hydroxyls, deactivated onto hexachlorocyclophosphazene which served to build the core. Quaternization of the stars containing six outer pyridyl groups created positive charges at their periphery while the acidic treatment of stars carrying terminal ketal rings afforded six arm PEO stars with 12 peripheral hydroxyls. The latter compound was subsequently deprotonated and used to polymerize ethylene oxide by a classical core-first approach. This resulted in the formation of highly branched PEO's also referred to as dendrimer-like PEO stars which consisted of a first generation of six PEO arms and a second generation of 12 hydroxy-ended PEO branches.