Boric acid polyesters

Boric acid esters provide for thermal stabilization of low-pressure polyethylene to a variable degree (Table 7). The difference in efficiency derives from the nature of polyester. Boric acid esters of aliphatic diols and triols are less efficient than the aromatic ones. Among polyesters of aromatic diols and triols, polyesters of boric acid and pyrocatechol exhibit the highest efficiency. Boric acid polyesters provide inhibition of polyethylene thermal destruction following the radical-chain mechanism, are unsuitable for inhibition of polystyrene depolymerization following the molecular pattern and have little effect as inhibitors of polypropylene thermal destruction following the hydrogen-transfer mechanism. 

The inhibitive efficiency of boric acid polyesters differs greatly. The highest efficiency is exhibited by polyesters of boric acid, aromatic diols and triols. This derives from the fact that in this case the radicals are accepted not only by boron, but also by the aromatic nucleus. Among the aromatic polyesters, most efficient is ester of boric acid and pyrocatechin due to the Frank-Rabinovich cage effect. The efficiency of inhibi-... 

Table 7 Inhibition of Polyethylene Thermal Destruction by Boric Acid Polyesters...

Boron complex azo dyes have also been reported. These include solvent soluble boron complexes, such as the red dye (32) used for dyeing polyester and coloring plastics25,26 and water-soluble dyes for the detection of boron (as boric acid) by a color change27 (Scheme 5). 

Finally, the water-soluble polyesters of phosphoric or boric acid with glycols or glycerol should be mentioned. They can be used in combination with water-soluble polymers like polyvinyl alcohol, polyacrylamide, and polyvinyl pyrrolidone. 

Borates Zinc borate, barium metaborates, ammonium fluoroborate, boric acid Flexible PVC, polyolefins, unsaturated polyesters, thermoplastic polyesters, epoxies, nylons, urethanes, and phenolics Alcan, Amspec Chemical, Asahi Denka Kogyo, Borax, Buckman Laboratories, Great Lakes... 

The polyesters prepared using the adduct of pentaerythritol and methyl azelaaldehydate (2,4,8,10-tetraoxaspiro[5,5]undecane) can be used to give cross-linked rubbery polymer gels by heating with such catalysts as zinc oxide, zinc acetate, litharge, boric acid, and /7-toluenesulfonic acid (see Fig. 1). 

Major use as a flame retardant is in PVC and halogenated polyester, usually in conjunction with antimony trioxide. Some would regard it as a partial replacement for antimony trioxide but it does have other benefits, most notably as an excellent after-glow suppressant. It is often used in combination with other flame retardants such as ATH. It also finds some use in flame retarding ceUulosics, where its greater resistance to water compared with borax or boric acid is needed. Total world use of zinc borate as a flame retardant may be around lOOOOtpa. 

Isophthalic polyesters have a relatively wide range of corrosion resistance. They are satisfactory for use up to IZST (52 C) in adds such as 10% acetic, benzoic, boric, citric, oleic, 25% phosphoric, tartaric, 10-25% sulfuric, and fatty acids. 

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