AbstractPyrolysis gas chromatographic studies were carried out on two polyphosphate esters of bisphenolASystematic name: 2,2′‐isopropylidendiphenol.. The gaseous pyrolysis products were found to be mainly phenols and a few phosphate compounds. The identification of phosphorus compounds in the gas phase proves a gas phase mechanism of flame retardant action for polyphosphates. The presence of phosphoric acid in the char residue supports the existence of the conventional condensed‐phase mechanism. Thus, the study demonstrates that both condensed‐phase and gas‐phase mechanisms are operative in the flame‐retardant action of pol