Abstract
Phenol was esterified with boric anhydride and the reaction products were polycondensed with paraformaldehyde. The higher was the boric anhydride content to phenol, the higher was the esterified content of the product. As the boron content of phenyl borate increased, the adequate amount of paraformaldehyde decreased.
Flexual strength of the cured resin strongly depended on the boron content. The strength gradually decreased with increasing heat treatment temperature. However, flexual modulus was hardly affected by boron content or by heat treatment temperature.
From the results of differential scanning calorimetry, both high temperature and long time were necessary to cure perfectly the phenyl borate resins. In order to explain these curing behaviors, frontier electron density calculations were carried out with triphenylborate (as a model for phenyl borates) and phenol. It was found that phenol showed high reactivity at both ortho and para positions, while triphenylborate had high reactivity only at para position.
