Triphenyl borate was prepared by reaction of boric acid with phenol in xylene. Its reaction with 1,3,5-trioxane involved replacement of protons in the para positions of the benzene rings by methylene group.Triphenyl borate (I) is used as a weak Lewis acid and complexing agent toward nitrogen-containing compounds. It also attracts interest as model compound for the preparation of poly(methylenetriphenyl borates). Published data on the properties of triphenyl borate (I), in particular on its melting point, are strongly different [1][2][3]. Several procedures for the preparation of triphenyl borate (I) have been reported. It can be obtained by esterification of boric acid with excess phenol in methylene chloride, followed by separation of phenol-water mixture by fractional distillation. Compound I is also synthesized by exchange reactions of boron trichloride with phenyl acetate at -80°C or of boric acetic anhydride with phenol with subsequent distillation of the resulting mixture at 360°C. We believe that the most convenient procedure is based on the reaction of boric acid with 3 equiv of phenol in o-xylene with simultaneous removal of water as azeotrope [3].The goal of the present work was to synthesize pure triphenyl borate (I) and examine its reaction with 1,3,5-trioxane (II) as a model process in the preparation of heat-resistant polymeric boric acid methylenephenyl esters. Reactions of phenols with formaldehyde are commonly carried out in a solvent. A classical procedure implies polycondensation of phenols or boric acid phenyl esters with 1,3,5-trioxane or paraformaldehyde in xylene under an inert gas [3][4][5][6]. We examined polycondensation of triphenyl borate (I) with 1,3,5-trioxane (II) using boron trifluoride-ether complex as catalyst and xylene as solvent (Scheme 1).Triphenyl borate (I) becomes liquid above 101°C. We also performed its reaction with trioxane in melt, following a procedure analogous to the synthesis in
An investigation was made of the interaction of new heat-resistant boron-containing polymers (polyesters of phenols and boric acid) with epoxy resin. A mechanism of this interaction is proposed, consisting in the formation of bonds between carbon of the epoxy group and carbon located in the o-position of phenyl radicals of the polymers.
The possibility is shown of controlling the strength and wear resistance of polymer friction materials based on rubbers by adding boric acid polymethylene-p-triphenyl ester without altering the basic production technology of the composites. The greater heat resistance of the modified friction composites is established.
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