Mechanism of thermal degradation of aryl bisphosphates and the formation of polyphosphates

Abstract

The thermal degradation of resorcinol bis(diphenyl phosphate) (RDP) and bisphenol A bis(diphenyl phosphate) (BDP) has been studied by 31P NMR, Q-TOF, and GPC at normal and extreme heating conditions. The thermal degradation begins with the elimination reaction that generates reactive monomers and arynes. The aryne-bisphosphate adducts or their decomposition products were identified through Q-TOF analysis. Through the intertwined condensations, transesterifications, and elimination reactions, the reactive acid phosphates are formed and eventually convert the bisphosphates into volatile triphenyl phosphate, oligomeric aryl/acid polyphosphates, and non-volatile polyphosphoric acid. It is these reactions and products that provide the bisphosphates effective pathways for entry into the vapor phase or action in the condensed phase. The facility of these reactions, particularly the elimination reaction that is the initiation step, to occur is critical for the high efficiency of flame retardancy displayed by the bisphosphates. A thermal Melvin rearrangement of the bisphosphates to arylphosphonates has also been established.