Borate system

A number of reviews have appeared covering the various aspects of borate glasses. The stmcture, physical properties, thermochemistry, reactions, phase equihbria, and electrical properties of alkah borate melts and glasses have been presented (73). The apphcation of x-ray diffraction, nmr, Raman scattering, in spectroscopy, and esr to stmctural analysis is available (26). Phase-equihbrium diagrams for a large number of anhydrous borate systems are included in a compilation (145), and thermochemical data on the anhydrous alkah metal borates have been compiled (17). 

According to the ethylene consumption rate profile for ethylene/l-hexene copolymerization in figure 1, it indicated that deactivation of active species occurred in the borate system. On the... 

The characteristics of C NMR spectra for all copolymers were similar. The triad distributions for all copolymo" from NMR monomer insertion are shown in Table 2. Based on the triad distribution of ethylene/l-hex aae copolymers in Table 2, we found that microstructurc of copolymer obtainrai fiom aluminoxane system was slightly different in monomer incorporation, but found significantly when borated system was applied. We suspected that this difference was arising fiom the diffaences in bimetallic complex active species between [aluminoxane] [catalyst] and [Borate] [catalyst] which had the electronic and gMmetric effects fiom the sterric effect of larger molecule of borate compare to the aluminoxane on the behaviors of comonomer insertion in our systems. 

Anions of weak acids can be problematic for detection in suppressed IEC because weak ionization results in low conductivity and poor sensitivity. Converting such acids back to the sodium salt form may overcome this limitation. Caliamanis et al. have described the use of a second micromembrane suppressor to do this, and have applied the approach to the boric acid/sodium borate system, using sodium salt solutions of EDTA.88 Varying the pH and EDTA concentration allowed optimal detection. Another approach for analysis of weak acids is indirect suppressed conductivity IEC, which chemically separates high- and low-conductance analytes. This technique has potential for detection of weak mono- and dianions as well as amino acids.89 As an alternative to conductivity detection, ultraviolet and fluorescence derivatization reagents have been explored 90 this approach offers a means of enhancing sensitivity (typically into the low femtomoles range) as well as selectivity. 

During the time of the Olin reports, the first examples of oligomeric boron-bridged (l-pyrazolyl)borate systems appeared from the laboratory of Trofimenko at DuPont Chemicals 24 He reported the synthesis of poly(l-pyrazolyl)borates (6) (Fig. 5) from the reactions of alkali metal borohydrides with the pyrazole ligand. The (l-pyrazolyl)borate ligand was obtained from two pyrazole units when bridged by a BR2 unit on one side and by a metal or onium ion on the other. Even though reports... 

A disadvantage of borane and borate systems is that the alkylmetallocene cations are more instable and more sensitive to impurities and water. To overcome this higher sensitivity, a dialkyl species can be build by an in situ reaction with tri-isobutylaluminum (TIBA). TIBA acts as alkylation reagent and as a scavenger and stabilizes the dialkyl species in solution it is used as stock solution for the polymerization experiments (Fig. 12). 

The two lower pH levels were phosphate buffers whereas the 8.6 buffer consisted of a boric acid, sodium borate system. The buffers showed no reaction with pretreatment chemicals used, and had sufficient buffer capacity to maintain constant pH during experiments of long duration. 

Very similar kinetics were observed with (SBI)ZrCl2/MAO although this catalyst is an order of magnitude less active, the concentration of active species turned out to be almost identical to the borate system kp/kp P = 0.08, with a similar accumulation of dormant states. Evidently the counteranion ([CN B(C6F5)3 2] vs. [Me-MAO] ) modulates the energetics of the chain growth cycle, i. e. the anion is intimately involved in the transition state, but does not influence the distribution between active and dormant states (Scheme 8.34) [97]. 

Retention time for formate ion using the borate system is 11 minutes at a flow rate of 2.3 mL/min. Fluoride, chloride, sulfate and acetate do not interfere in the analysis. Linear response is obtained over the concentration range of 0.1-4 yg/mL. The detection limit is estimated at 0.05 yg/mL for an injection volume of 100 yL at 3 ymhos full scale sensitivity. 

Wise, E.T. and S.G. Weber, A simple partitioning model for reversibly cross-linked polymers and application to the poly(vinyl alcohol)/borate system ("slime"). Macromolecules, 1995. 28(24) p. 8321-8327. 

In studies with amino acids and similar compounds, the ligand is nearly always monomeric. This situation changes greatly in those cases where the ligand can form dimers and higher condensation n-mers, such as phosphate (20), borate (21, 22, 23), and where polynuclear species are possible, such as with the copper (II) ion (24) and the Fe(III)ion (25). To extend these studies and to consider the analyses of other types of systems that reversibly form complexes, the mannitol-borate system which has previously been studied (26, 27), but without taking all forms of the borate ligands into account was examined. 

Another example is Figure 2, which is a diagram for a sample of sea water (7). It shows the log (concentration) for the species in the carbonate system (H2C, HC, C-") and the borate system (HB, B") at various pH. At the log [H ] of the sea water sample, one may read the concentrations of the two predominating species (HCO and H BO 0 and of the minor species. One can also determine the change in concentrations as the [H ] is altered—e.g., by adding acid. It is immediately obvious that there will be two equivalence points (points of minimum buffer capacity), namely, Pi and P2. 

Many magnesium borate systems have been investigated a few of the major studies are listed in Table VII. The main magnesium borates stable in contact with aqueous solutions are the 1 1 3 (pinnoite), 1 3 x, 2 1 1, and 2 3 15 (inderite) compounds. 

The lack of data on certain metal borate systems has been implied in Section V. Quite apart from thallium, zinc, and lead compounds, the range of known borates of barium and strontium is somewhat limited. There are no obvious reasons why the latter should not have stability ranges approaching those of calcium and magnesium borates. Clearly, more investigations are necessary in this area. 

Wegh et al. (2001) studied the Nd3+ emission spectra for several phosphate and borate systems upon VUV excitation of the 4f25d levels. They observed 4f25d 4f3 fluorescence from... 

A great advantage of the borates is that the ratio of borate to metallocene is about 1 to 1 and not 5000 to 1, as in the case of MAO for homogeneous systems. On the other hand, the borate system is highly sensitive to poisons and decomposition and must be stabilized by addition of aluminum alkyls such as triisobutylaluminum (TIBA) the necessary ratio of TIBA to zirconocene is in the range of 100-500. 

Red light is obtained by either Y2C>3 Eu or (Y,Gd)B03 Eu, the VUV absorption of Y2C>3 Eu is weaker than that of (Y,Gd)B03 Eu but the emission spectrum of Y2C>3 Eu better matches the EBU requirements for display applications. The emission spectrum of Y2C>3 Eu has a maximum at 611 nm while that of the borate system is at 595 nm. This illustrates the point that although the emission spectrum of Eu3+ is due to optical f-f transitions, the detailed shape of the emission spectrum depends on the crystal host. Emission in Y2C>3 Eu at 611 nm is due to an electric dipole transition while in the case of... 

The main principles of anhydrous borate systemics are that... 

Acid-Base Properties of Anhydrous Borate Systems... 

Numerous anhydrous borate structures can be reduced to various combinations of three types of basic structural units 1) fundamental structural units, 2) combined basic structural units, and 3) full radicals of polyanions. The stability of the FSU, CSU and CRP units in solid and liquid borates is one of the most important issues, and will provide a better understanding of, and control of, phase formation in complex borate systems. 

In the initial description of the cationic dye-borate system [24, 76], it was postulated that electron transfer was possible because, in nonpolar solvents, dye/borate salts exist predominantly as ion pairs. Since the lifetime of the cyanine singlet excited state is quite short [24, 25], this prerequisite is crucial for eflfective photo-induced electron transfer. Recently initiator systems in which neutral dyes are paired with triarylalkylborate anions have appeared in the literature [77]. In the latter case, the borate ion acts as the electron donor while neutral merocyanine, coumarin, xanthene, and thioxanthene dyes act as the electron acceptors. It is obvious that these initiating systems are not organized for effective electron transfer processes. The formation of an encounter complex (EC) between excited dye and electron donor is required. 

Evans (1.) analyzed the enthalpies of formation of the lead borate system. Shartsls and Newman measured enthalpies of solution of the lead borate glasses In 2 N HNO. In their phase studies, Mazzettl and De Carll (3) established that the compounds formed were PbO BgOg, Pb0 2Bg0g and 2 PbO bBgOg. Prom the Shartsls and Newman (2) paper, Evans (1 ) obtained the following ... 

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