Structure and thermal pyrolysis mechanism of poly(resorcinol borate) with high char yield

Boron-containing organic polymers have excellent thermal stability and flame retardancy. Hyperbranched polymers, in which boron atoms are introduced in the form of borates, exhibit superior performance and have more applicability. This work focuses on the boron-containing polymer poly (resorcinol borate) (PRB). The chemical structure of PRB and its structural evolution at high temperatures are investigated in order to clarify the reason for its high char yield. The results indicate that the molecular skeleton of PRB mainly consists of aromatic structures, borates, B—O—B structures, and a small number of boron hydroxyl groups and phenolic hydroxyl groups. During pyrolysis, boron oxide is formed by the cleavage of borate O—C bonds at about 400 °C. This process effectively avoids the formation and release of volatile carbon dioxide, reducing carbon loss. A large fraction of the carbon from aromatic rings is converted to amorphous carbon via pyrolysis, which possesses higher thermal stability. These results can guide the design and synthesis of novel boron-containing polymers and can provide a strategy for modifying the thermal properties of phenolic resins in order to broaden their applicability in the field of ablative-resistant composites and coatings.