Ru-doped phosphazene membrane materials used for catalytic hydrogenation

Semicrystalline polydimethylphosphazene [-N=P(CH3)2-]n (PDMP) and the catalyst Ru-doped PDMP, in both the virgin and hydrogenated forms, have been analysed using differential scanning calorimetry spectroscopy (DSC), 31P magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, powder X-ray diffraction (XRD) and positron annihilation lifetime spectroscopy (PALS). These techniques in combination indicate that the catalyst Ru coordinates the polymer and alters the structural conformation of the polymeric chain. The PALS data show that this coordination induces structural ordering that results in a decrease in the size of the inter- and intra-chain spacing. This ordering is also evidenced by a decrease in the intensity of the 31P upfield resonance, an increase in Tg and the appearance of a pre-melting endotherm.

The pure host polymer, poly(dimethylphosphazene), PDMP, and the ruthenium, Ru, catalyst doped PDMP in both the virgin and hydrogenated form (spent catalyst) were studied to try to understand the role of the polymer in complexing the Ru ion. Comparison of NMR, XRD and PALS results showed that the catalyst Ru occupies the inter- and intra-chain nanospace available in pure PDMP and affects the structural conformation of the polymeric chain. In addition the PALS results show that the Ru ion not only fills the nanospace but also induces structural compacting due to coordination with the polymer. In view of these promising results, further studies are in progress to further define the effect of Ru addition on the microstructure of the polymer and its preferred conformation as these characteristics may be critical to the rate of hydrogenation.