Thomas A. Luther

Characterization of gas transport in selected rubbery amorphous polyphosphazene membranes

Gas permeabilities for six different gases have been evaluated for a series of closely related polyphosphazenes. Polyphosphazenes are attractive polymers for use as gas separation membranes due to their inherent chemical, thermal, and radiation stability. Additionally, polyphosphazenes may be tailored for specific chemical affinities. In this report, polyphosphazenes with three different pendant groups with varied hydrophilicity were characterized for gas permeation. All polymers were characterized as having modest permeabilities for methane, oxygen, nitrogen, helium, and hydrogen. These gases were not observed to have a significant interaction with the polymer structure and transport is attributed to segmental chain motion. Carbon dioxide was found to have a significant intermolecular interaction with the polymer and the permeability was observed to be proportional to the percentage of hydrophilic 2-(2-methoxyethoxy)ethanol on the backbone. Thus, we report a promising method for the development of CO2 selective membranes.

Selective Extraction of Minor Actinides from Acidic Media Using Symmetric and Asymmetric Dithiophosphinic Acids

The minor actinides (Am and Cm) and other transplutonium elements represent significant, long-term hazards found in spent nuclear fuel. The selective extraction of the minor actinides from the lanthanides is an important part of advanced reprocessing of spent nuclear fuel. This separation would allow the minor actinides to be fabricated into a target and recycled to a reactor and the lanthanides to be disposed. Due to the similarities in the chemical properties of the trivalent actinides and lanthanides, this separation is difficult to accomplish. The introduction of soft donor groups, such as N or S, into similarly structured ligands increases the differentiation between An(III) and Ln(III) cation coordination. Partly because of limitations imposed by synthetic methodologies, previous studies of dithiophosphinic acid (DPAH) extractants has been restricted to a comparatively small number of symmetrical dialkyl and diaryl derivatives. Research efforts at the Idaho National Laboratory have resulted in the recent development of an innovative synthetic pathway yielding new regiospecific DPAH extractants. The synthesis improves DPAH designs that can address the issues concerning minor actinide separation efficiency and extractant stability. Several new symmetric and asymmetric DPAH extractants have been prepared. The use of these extractants for the separation of minor actinides from lanthanides will be discussed. In addition, the variation in the extent of Am(III) extraction by a related series of DPAH isomers will be presented.

Formation of pervaporation membranes from polyphosphazenes having hydrophilic and hydrophobic pendant groups: Synthesis and characterization

A series of new polyphosphazene polymers were synthesized using three different pendant groups with the goal of probing structure-function relationships between pendant group substitution and polymer swelling/water flux through thin dense films. Formation of polymers with relative degrees of hydrophilicity was probed by varying the stoichiometry of the pendant groups attached to the phosphazene backbone: p-methoxyphenol, 2-(2-methoxyethoxy)ethanol, and o-allylphenol. The polymers in this study were characterized using NMR, thermal methods, and dilute solution light-scattering techniques. These techniques revealed that the polymers were amorphous high polymers (M w = 10 5 -10 7 ) with varying ratios of pendant groups as determined by integration of the 1 H- and 31 P-NMR spectra. Thin dense film membranes were solution-cast with azo-bis(cyclohexane)carbonitrile included in the matrix and crosslinked using thermal initiation.

Synthesis and Characterization of Mixed-Substituent P- n -Propyl-N-trimethylsilylphosphoranimines

One approach to the synthesis of polyphosphazenes is the condensation polymerization of phosphoranimines. In this work, several novel P-n-propyl-N-trimethylsilylphosphoranimines have been synthesized and characterized. Modifications to the literature synthetic routes were required to obtain the precursor phosphines. The N-trimethylsilylphosphoranimines were obtained though oxidation of the phosphine with bromine and then subsequent nucleophilic displacement using lithium phenoxide. These phosphoranimines were stable for long periods of time under dry inert conditions. NMR analyses revealed complex splitting patterns beyond typical coupling due to the stereocenter at phosphorus. We report several approaches to the n-propyl containing phosphines and phosphoranimines.

Reactions and polymerization of hexa-[3-tert-butyl-4-hydroxyphenoxy]cyclotriphosphazene : A new method for the preparation of soluble cyclomatrix phosphazene polymers

Novel cyclomatrix phosphazene-containing polyester polymers were synthesized through the reaction of a polyhydroxylated cyclotriphosphazene and a bifunctional acid chloride. To demonstrate the chemistry of the free hydroxyl of hexa-[3-tert-butyl-4-hydroxyphenoxy]cyclotriphosphazene, nucleophilic displacement reactions were performed with both acetic anhydride and alkyl chlorides. This work compares favorably to literature data for the chemistry of hexa-[4-hydroxyphenoxy]cyclotriphosphazene, whose hydroxyl is not hindered by an adjacent substituent. The hindered site of hexa-[3-tert-butyl-4-hydroxyphenoxy]cyclotriphosphazene was found to react with bidentate acid chlorides to yield new high polymers. The phosphazene-containing polyesters were observed to have good solubility in polar organic solvents. Characterization of these new materials was performed using dilute solution laser light scattering techniques, thermal analysis, and NMR spectroscopy.

Fundamental Chemistry of the Universal Extractant (UNEX) for the Simultaneous Separation of Major Radionuclides (Cesium, Strontium, Actinides, and Lanthanides) from Radioactive Wastes

Scientists at the INEEL and KRI collaboratively developed and validated the concept of a Universal Extractant (UNEX) for simultaneously removing the major radionuclides (Cs, Sr, actinides, and lanthanides) from acidic radioactive waste in a single solvent extraction process. The UNEX solvent incorporates three active extractants: chlorinated cobalt dicarbollide, polyethylene glycol, and a carbamoylmethylphosphine oxide derivative, dissolved in a suitable organic diluent to simultaneously extract target radionuclides. The process chemistry is unique, but complicated, since the extractants operate synergistically to extract the radionuclides. Furthermore, interactions with the diluent are quite important as the diluent strongly influences the extraction properties of the solvent system. We are currently studying the fundamental chemical phenomena responsible for the selective extraction of the different species to understand the underlying mechanisms and facilitate enhancements i n process chemistry. Our efforts to date have relied on a combination of classical chemistry techniques, infrared (IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy to identify and explain the structures formed in the organic phase, elucidate the operative chemical mechanisms, and evaluate the diluent effects on extraction properties.

Water Transport Polymers – Structure/Property Relationships of a Series of Phosphazene Polymers

A study was undertaken to explore the water passing properties of a series of phosphazene polymers versus the attached pendant group structure. Pendant groups containing different numbers of ethyleneoxy groups were synthetically attached to the backbone of phosphazene polymers. Phosphazene polymers facilitate these types of studies because, during their synthesis, the polymer backbone is formed first and then the desired pendant groups are attached through nucleophilic substitution. For these studies, four polymer series were synthesized and tested for their water passing properties. The polymers contained different amounts of ethyleneoxy units. Two different polymer families were synthesized and compared in this work. The critical difference in the two polymer series is that one contained pendant groups with aromatic rings, in addition to the oligioethyleneoxy moieties, while the other has no aromatic rings in its structure. Polymers with phenyl group-containing pendant groups exhibited poor water permeability if they possessed fewer than six ethyleneoxy units. Polymers with more than six ethyleneoxy units inserted between the phenyl ring (tail) and the polymeric backbone exhibited reasonable water permeability. Two additional series of polymers with mixed pendant groups were synthesized and the water passing properties of the phosphazenes varied in proportion to the hydrophilic to hydrophobic balance induced by each individual pendant group. A final study of polymers with shorter pendant groups demonstrated the effect of pendant group on water permeability. These studies suggest that the polyphosphazenes may be tailored for specific water passing applications.

Comparison of Aromatic Dithiophosphinic and Phosphinic Acid Derivatives for Minor Actinide Extraction

A new extractant for the separation of actinide(III) and lanthanide(III), bis(otrifluoromethylphenyl) phosphinic acid (O-PA) was synthesized. The synthetic route employed mirrors one that was employed to produce the sulfur containing analog bis(otrifluoromethylphenyl) dithiophosphinic acid (S-PA). Multinuclear NMR spectroscopy was used for elementary characterization of the new O-PA derivative. This new O-PA extractant was used to perform Am(III)/Eu(III) separations and the results were directly compared to those obtained in identical separation experiments using S-PA, an extractant that is known to exhibit separation factors of ~100,000 at low pH. The separations data are presented and discussed in terms comparing the nature of the oxygen atom as a donor to that of the sulfur atom in extractants that are otherwise identical.