SANS Investigation and Conductivity of Pure and Salt-Containing Poly(bismethoxyphosphazene)

Abstract

Poly(bismethoxyphosphazene) (PBMP) was synthesized, giving polymer melts with T g ) -70.9 °C. The chain dynamics of melts and DMF solutions of poly(bismethoxyphosphazene) (PBMP) was investigated by Small-Angle Neutron Scattering (SANS). The radius of gyration R g was found as 144.7 ( 0.2 Å, and the average MW from SANS was 95000 Da. DMF revealed to be a good solvent for this polymer. From the scattering intensity of polymer solutions for high q-data, the slope was -1.647 in almost exact agreement with the expected excluded volume exponent by Flory which is 5 / 3 affirming the good solvent property of DMF. GPC measurements of THF solutions were evaluated based on a universal calibration of polystyrene standards resulting in a rather similar value of 1.05 × 10 5 Da. Another series of SANS experiments was done with solutions of LiSO 3 CF 3 (LiTf) in the title polymer. They also showed low T g values down to -50 °C at 15 wt %. The SANS results (5 and 10 mol % LiTf as referred to the monomer units) showed almost no effect of the dissolved salt on the melt conformation of the polyphosphazene (almost random coil), and thus revealed a rather small interaction between salt and polymer. We also measured the ionic conductivity of salt-in-polymer systems with concentrations from 5 to 20 wt % LiTf. The room-temperature conductivity was 1.7 × 10 -5 S/cm at 20 wt % LiTf and is thus rather high. The low interaction between salt and polymeric solvent is in agreement with the predominance of neutral ion pairs which is often observed in such polymer electrolytes.

Dynamics of a Polyphosphazene Melt Studied by Solid-State 2H NMR

“…As expected for glass-forming polymer melts, all data are consistently described by the Vogel−Fulcher−Tammann (VFT) equation τ = τ 0 exp true[ B T − T 0 true] where B = 1150 K and T 0 = 170 K. In previous studies, a VFT temperature dependence was also observed for the α-process of polyphosphazenes featuring bulkier side groups, − e.g., for poly[bis(trifluorethoxy)phosphazene] (PFEP). Extrapolating the present VFT fit to lower temperatures, a correlation time of τ ≈ 100 s is reached in the vicinity of the calorimetric glass transition, T g = 191 K, confirming that the STE experiments probe the α-process. In agreement with this conclusion, reinspection of Figure shows that the observed dynamical process leads to a complete decay of F 2 , as expected for isotropic reorientation associated with the α-process, while restricted reorientation typical of a β-process would leave a finite residual correlation at t m ≫ τ.…”

“…Synthesis and characterization of the studied PBMP- d 6 were described in ref . A molecular weight of M w = 1.04 × 10 5 g/mol and a glass transition temperature of T g = 191 K were reported.…”

“…For a fundamental understanding, it is important to investigate the behaviors of the phosphorus-nitrogen backbone, i.e., to use small substit-uents, and to compare the results for inorganic and organic backbones. Recent work 8 utilized poly[bis(methoxy)phosphazene] (PBMP) as a model polymer to study thermodynamic and structural aspects. Here, the dynamics of this polyphosphazene are characterized in some detail using 2 H NMR.…”

Salt-in-Polymer Electrolytes for Lithium Ion Batteries Based on Organo-Functionalized Polyphosphazenes and Polysiloxanes

“…However, the mobility of the polymer segments is enhanced. SANS measurements support this: the BMP molecules in the liquid polymer behave like statistical coil molecules [41]. Therefore, it is not surprising that the conductivities of salt solutions in BMP are as high as those of MEEP with dissolved lithium triflate.…”

Inorganic and organometallic polymers

“…83 The conductivity of salt-containing poly(bismethoxyphosphazene) has been evaluated. 84 The functionalization of polyamide-and polyvinylalcohol-surfaces with polydichlorophosphazene which was later functionalized by 2,2,2-trifluoroethanol has been reported. 85,86 The hydrophobic properties of these surfaces was probed through surface contact angle measurements.…”