High char yield of aryl boron-containing phenolic resins: The effect of phenylboronic acid on the thermal stability and carbonization of phenolic resins

This work reports an aryl boron-containing phenolic resin (PR) exhibiting an extremely high thermal decomposition temperature and char yield and formed by reacting phenylboronic acid (PBA) with PR. DSC was used to study the curing behaviour of the PBA modified PR (PBPR). The structure and thermal properties of the cured PBPR were investigated by FTIR, XPS, 11B NMR and TGA. Phenylboronates were formed during the curing of PBPR, which reduced the distance between benzene rings. The TGA indicates that the temperature with the maximum decomposition rate increased for the cured PBPR by 56 °C, and the charring yield increased by 13.4 per cent (800 °C, nitrogen atmosphere) relative to PR. FTIR, XPS, XRD, 11B NMR and Raman analyses were used to study the structural evolution of the cured PBPR during pyrolysis. Boron oxide was formed during the char formation from the cleavage of B-C and B-O-C bonds via pyrolysis, which effectively avoided the release of volatile carbon oxides and retained the carbon. In addition, incorporating boron into the carbon lattice increases the crystallite height and decreases the interlayer spacing. These findings reveal that PBA exhibited obvious effects in improving the thermal stability and promoting the graphite crystallites of PR during carbonization.