Uranyl polymers

NMR measurements also provide information on the coordination of the ligands in the uranyl polymers. Solid-state I c-NMR confirms the coordination modes of the carboxylate ligands to the uranyl ion that is, both monodentate and bidentate carboxylate coordination modes are evident. The uranyl dicarboxyl ate polymers which possess two moles of coordinated DMSO exhibit two carbon-13 carbonyl resonances, one at about 175 ppm downfield from tetramethylsilane (TMS) and one at about 185 ppm. The polymers which possess only one mole of coordinated DMSO exhibit only the carbonyl peak near 185 ppm. Based on other known coordination compounds, the 175 ppm peak can be assigned to monodentate carboxylate and the 185 ppm peak to bidentate carboxylate. Thus, 7-coordination predominates in the polymers with either one or two moles of solvent coordinated to the uranyl ion, which is consistent with the infrared results reported elsewhere (5). 

Before leaving consideration of this group of compounds, mention should be made of one unusual species of this general class. Tabushi, Kobuke and Nishiya have reported a polymer-bound hexaketone, illustrated below as compound 29, which is apparently of use in binding uranyl (UO2++) ions. The polymer has, in fact, been utilized in extraction of the uranyl ion directly from seawater . 

Uranyl Nitrate Influence on Polymer Growth. The effect of a solute such as uranyl nitrate on this polymer formation is so complex that the net effect on the polymer growth rate cannot be predicted. Experimentally, it is observed that the rates of growth at given initial HNO3 concentration are always slower in the presence of as indicated by the solid curve in... 

Chemical analyses reveal that measurable amounts of uranyl ion are actually present in Pu(IV) polymers grown in mixtures of Pu(IV) and uranyl nitrate suggesting that uranyl ion is being taken up in the polymer network and consequently hampers the growth through a chain termination process as suggested in Fig. 3. The uranyl serves to terminate active sites because it does not typically form extensive polymeric aggregates as does Pu(IV) instead it tends only to dimerize and, at most, tri-merize (4). 

PuI3C2H 4 4THF and PuI2C2H3 46-48 Bond, uranyl-to-Pu(IV) polymer,... 

A second method of solving the kinetics dilemna consists of driving a polymerization reaction to completion by removing a volatile coproduct as in the case of uranyl dicarboxylate polymers from uranyl acetate and the dicarboxylic acid (5) ... 

Polymer and copolymer. Polymer and copolymer were prepared in our laboratory for strict control of purity, branching content and molecular weight. All monomers and solvents were carefully purified. PVC samples were prepared as powders in bulk using free radical photoinitiation with either AIBN or uranyl nitrate as initiators. The AIBN/UV initiation was used for photopolymerization at temperatures of 50°, 25°, and 0°C. 

Two types of initiator were used in this work, AIBN and uranyl nitrate. Unreacted initiator was thoroughly removed from the polymer. A comparison of PVC samples prepared by the two different initiators showed identical behavior under ESR investigation. Therefore, end groups derived from the initiator do not appear to affect the course of degradation appreciably. 

The proof of the chain terminating function of U02 could be obtained by the identification of a uranyl-to-pol3nner bond through the usage of Raman spectroscopy. However, Raman spectra of plutonium solutions are difficult to measure since the solutions must be kept in alpha-containment boxes we, therefore, have turned to polymer solutions of Th(IV) in place of Pu(IV) for the initial studies. It is through the decrease in the frequency of the symmetric stretching vibration... 

Block copolymers, in w hich one part of the chain is made up entirely of residues of one type, the next part entirely of the other sort, and so on, can be conveniently made by emulsion methods (62). For example, if only the monomer A is water-soluble, the polymer radicals which are initially generated in this phase consist of short chain —A—A— A—A—A—A—. If these then diffuse to the phase boundary of droplets of the water-insoluble B monomer, further addition to the chain will occur to give the polymer B—B—B—B—B—B—A—A—A—A—A—A— B—B—B—B—B—B—B. This is the required block copolymer. As an example of this type of polymerization, acrylic acid ( A ) and styrene ( B ) give a block copolymer if the initial polymerization in the aqueous phase is catalyzed by the photosensitizer uranyl nitrate. 

A number of excellent review articles on MOFs and coordination polymers have appeared in the literature recently. " We will therefore limit our introduction to a discussion of essential structural issues necessary to appreciate this class of inorganic/organic hybrid materials. We will also point out that to the best of our knowledge, this is the first review of uranyl containing... 

Table 1. Uranyl coordination polymers constructed from oxalate linkages.

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