Poly borates, formation

Alumina trihydtate is also used as a secondary flame retardant and smoke suppressant for flexible poly(vinyl chloride) and polyolefin formulations in which antimony and a halogen ate used. The addition of minor amounts of either zinc borate or phosphoms results in the formation of glasses which insulate the unbumed polymer from the flame (21). 

Examination of the backbones of the neopentane-based, carbon-anchored TIME and bulky TIME tripodal ligands reveals possible reasons for the lack of 1 1 complex formation with metal centers. A hypothetical complex of TIME would contain three eight-membered rings (Fig. 9, I) with much lower stability than the more commonly observed five, six, or seven-membered rings formed, for instance, by poly(p5irazolyl)borate or poly(phosphine) ligands. In order... 

The outcome is more complex in the naphthalene series, where both the position of attack and the competition by rearomatization depend on the reagent chosen and conditions. Monocyanonaphthalenes are benzylated only by />-methoxytoluene, or by m- or />-methoxyphenylacetic acids, not by (poly)methylbenzenes [23,199]. 1,4-Dicyanonaphthalene reacts easily with toluene and a variety of precursors of the benzyl radical (alkylbenzenes [200-205], benzylsilanes, stannanes [206], and borates [56], as well as phenylacetic acids) [207] giving three types of products, viz. l-benzyl-4-cyanonaphthalenes, 1- or 2-benzyl-l,2-dihydro-l,4-dicyanonaphthalenes and dibenzobicyclo[3.3.1]nonanes resulting from the formation of a second carbon-carbon bond (Schs. 12 and 13). 

In some instances complexes were obtained derived from poly(l-pyrazolyl)borate ligands which never existed by themselves. This was the case with halogenation of the 4-position in HB[pz-3,5-(CH3)2]3Mo(CO)2NO to produce derivatives of the type HB[pz-3,5-(CH3)2-4-X]3Mo(NO)X2 and in HB[pz-3,5-(CH3y3Re(CO)3 which, on bromination, yielded the species HB[pz-3,5-(CH3)2-4-Br]3Re(CO)3 Another example is the formation of 20 by the reaction depicted in Eq. (7). 

A tris(imidazolyl)borate (138) complex of thallium(I) has been synthesized.The solid-state structure of hydrotris(imidazolyl)boratothallium(I) consists of one-dimensional, twisted, ladderlike strands, and three-coordinate thallium centers. Due to the position of the nitrogen donors, the tris(imidazolyl)borate ligand is not capable of forming metal chelates as are observed in tris(pyrazolyl)borates. Poly(benzotriazolyl)borate ligands have some features of both tris(pyrazo-lyl)borate and tris(imidazolyl)borate systems. Thallium(I) complexes of bis-, tris-, and tetrakis (benzotriazolyl)borates are reported. These adducts have been synthesized by treating the corresponding potassium derivative with an equimolar quantity of thallium(I) formate. ... 

In 1988 Lalor reported the synthesis and spectroscopic characterization of some new poly(benzo-triazolyl)borate salts (Scheme 8).180 The regiospecifity of the synthesis of I I B( Btz)4 differs from that of pyrazole/BH4 reaction in that B—N bond formation takes place in a manner that maximizes steric crowding at boron (i.e., at the triazole N(l) atoms). In 1989 Shiu describes some new metal carbonyls of HB(Btz)3.181 The synthesis and spectroscopic characterization of some first-row transition metal complexes was reported by Cecchi,182 whereas Hill described some new Rh183 and Ru184 carbonyl and isonitrile complexes. The formation of isonitrile derivatives was proposed to proceed through an associative mechanism involving an intermediate complex... 

Recently the complex formation between poly(vinyl alcohol) aikl borate was studied with the aid of Boron NMR. Sinton [191] concluded, in comparison with 2,4-pentanediol, to a didiol complex with a formation enthalpy of — 36 kJ/mol. As model species Shil yama et al. [192] made use of 2-firopanol and 2,4-pentanediol. It apprared that, first, a diol is needed for the formation of... 

Table 2. Thennodynatnic parameters oT the poly(vinyl alcohol)/borate didiol complex formation...

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. 

Gels are also obtained by the addition of borate to aqueous poly(vinyl alcohol) solutions. The tetrafunctional crosslinks, consisting of didiol bonds with borate, are of a dynamic nature, with time constants of the order of 0.01 to 10 s, depending on temperature. The heat of crosslink formation varied firom — 10 to — 20 kJ/(mol of crosslinks), which is much le than the values obtained in the gelation process of aqueous poly(vinyl alcohol) solutions, where it varied from — 37 to —168 kJ/mol, depending on the syndiotacticity of the poly(vinyl alcohol) used. 

The formation of a hydrogel upon mixing a poly(vinyl alcohol) (PVA) solution with a borax solution was reported more than six decades ago. Many other polyhydroxy polymers, such as poly(glyceryl methacrylate) and some polysaccharides,can also be gelled by borax. NMR spectroscopy studies indicated that the B(OH)4 anion binds to alternate OH groups on the polymer, especially when they are in the meso configuration. The nature of the crosslink is not absolutely clear, as there are proposals for the borate ion to link to both chains directly, while others have suggested that one of the links is via the sodium ion. ... 

It is well known that addition of a small amount of sodium borate, SB, to an aqueous solution of poly(vinyl alcohol), PVA, enhances the viscosity remarkably [7]. This is due to the formation of a complex between two ols, i.e. hydroxy groups and the borate anion, which plays a role of a transient cross-linker among the PVA chains. Similar behavior has been reported for several other polyhydroxy polymers such as poly(glyceryl methacrylate) [8] and polysaccharides [9-11]. 

Another condensation of hl -diiodoferrocene with a series of dialkynes has led to the formation of a series of poly(arylene-ethynylene) type polymers. Bifunctional ferrocene-based tris(l-pyrazolyl)borates have been used to obtain a range of inorganic polymers with ferrocene in the backbone-—see... 

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