Borate, poly -, alkali

Pyrazoles, and some indazoles, substituted on the nitrogen by B, Al, Ga, In, Si, Ge, Sn, P and Hg are known. Poly(pyrazol-1 -yl)borates have been studied by Trofimenko (72CRV497) who found that they were excellent ligands (Section 4.04.2.1.3(vi)). The parent ligands (282), (283) and (284) are available by the reaction of an alkali metal borohydride with pyrazole, the extent of substitution depending on the reaction temperature (Scheme 22). 

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... 

B. POTASSIUM HYDROTRIS(1 -PYRAZOLYL)BORATE— ALKALI METAL POLY(l-PYRAZOLYL)BORATES... 

Another approach which has been taken by many researchers for chain extension of polyesters is the use of di or poly-epoxy compounds. Diepoxides, usually of molecular weight between 100 and 1200 have been used, often with catalysts such as tetrasodium ethylenediaminetetraacetate [195], alkali metal halides [200], or alkali metal borates [207]. N,N -bis(glycidyl ester)pyromellitimides have been investigated [170, 171], as have digycidyltetrahydrophthalate [172], di- or poly-substituted diphenylpropane and related substances [205]. It has also been suggested that, for ease of handling and addition, such compounds may be combined with a titanium dioxide carrier [209]. 

Cheng and Rodriguez [195] demonstrated that the addition of boric add (H3BO3) to poly(vinyl alcohol) solutions has hardly any effect on the gelation properties. Addition of sodium hydroxide, by which NaB(OH)4 fe formal, results in gel formation. The maximum effect is observed for [Na ]/[B] = 1 addition of more sodium hydroxide has no effect Results are shown in Fig. 52, where logG is plotted vs added sodium hydroxide logG rises linrarly with added sodium hydroxide up to the point where the sodium/borate ratio is 1. From then on, the modulus is constant This confirms the Shibayama model [193], where Na is needed to form a crosslink. From the work of Kurokawa et al. [196] it became clear that the phase behaviour of the aqueous ix>ly(vinyl alcohol)/borate system not only depends on concentration of polymer and borate, but also on the addition of alkali hydroxide and of indifferent electrolytes like sodium chloride. 

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