Synthesis and characterization of a new hybrid polyphosphazene containing two symmetrical polyhedral oligomeric silsesquioxane (POSS) units

Abstract

A new hybrid polyphosphazene with two symmetrical polyhedral oligomeric silsesquioxane (POSS) (polyphosphazene-POSS) units was synthesized via the corner-capping reaction of incompletely condensed POSS ((c-C5H9)7Si7O9(OH)3) (POSS-OH) and poly[bis(2,2,2-trichloroethoxy)phosphazene] (polyphosphazene-Cl). Polyphosphazene-Cl was prepared via the chlorine replacement reaction of poly(dichlorophosphazene) and 2,2,2-trichloroethoxide. POSS-OH was synthesized through the hydrolytic condensation reaction of cyclopentyltrichlorosilane under reflux in aqueous acetone. Polyphosphazene-POSS was characterized using the 1H, 29Si and 31P nuclear magnetic resonance (NMR), fourier transform infrared, differential scanning calorimetry, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy techniques. This new polyphosphazene is a hybrid organic–inorganic polymer that possesses a backbone of alternating phosphorus and nitrogen atoms and two side-chain-tethered POSS pendant units as inorganic parts. The incorporation of POSS groups into the side chain of polyphosphazene improves the thermal stability of polyphosphazene-POSS because of the filler effect, and the crystallinity of polyphosphazene-POSS disappears because of the restriction of polymer orientation caused by the bulk and large volume of the POSS units. Polyphosphazene-POSS exhibit high storage stability against gelation compared with polyphosphazene-Cl. In addition, the introduction of the POSS units increases the hydrophobicity of polyphosphazene-POSS because of the enhanced hydrophobicity of the seven cyclopentyl groups attached to POSS. This new polyphosphazene is a hybrid organic–inorganic polymer that possesses a backbone of alternating phosphorus and nitrogen atoms and two side-chain-tethered POSS pendant units as inorganic parts. The incorporation of POSS units into the side chain of polyphosphazene improves the thermal stability of polyphosphazene-POSS because of the filler effect, and removes the crystallinity of polyphosphazene-POSS because of the bulk and large volume of the POSS units. Polyphosphazene-POSS shows high storage stability against gelation compared with polyphosphazene-Cl.